uHu
Bridgeburner
Re. testing the terminals of the ahc ecu, you probably mean this page:
which is under the "Diagnostics" chapter in the FSM. Here:
Definitive list of AHC maintenance items (4 Viewers)
- Thread starter yuji
- Start date
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Thank you #uHu.
Yes this is very helpful my friend.
However I was reading a more in-depth document a few weeks back. It was explaining how one had to sometimes test certain ports with the plugs in and others with the plug out. It explained how one had to slide the multimeter probe down the inside of back side of plug to get a contact.
I have gone through the manual a few times now and I can’t find this specific document.
I remember thinking at the time that this specific document was extremely helpful and that I must save it for future reference. It was specific to testing the AHC ECU.
I know I have it saved somewhere but pathetic as it is I have saved many notes over the past 6-8 months and I must not of identified or titled my saved note well enough resulting in my not being able to retrieve it. I will probably have to go through all my saved docs, as the one I’m looking for will be held within another note somewhere. All very convoluted I know.
Back at Post #941 in this thread, I referred to a long diagnostic story posted by @YvesNL – perhaps this is the thread which should be reviewed? All of this very well-illustrated thread is worthwhile reading:
Hi From The Netherlands & AHC Issues - https://forum.ih8mud.com/threads/hi-from-the-netherlands-ahc-issues.997849/
In particular in this thread, see Post #38 and Post #44. Then Post #45 goes on to describe the follow-up to ascertain the whereabouts of the fault in the circuit which has been tested. The approach here starts with the standards for each circuit connected to the ECU as set out in FSM DIAGNOSTICS section at Page DI-218 “TERMINALS OF ECU”, as already mentioned by @uHu. This method is useful in detecting problems in a given circuit as described in the example by @YvesNL and does not necessarily focus on a particular component.
The well-illustrated Posts #253 through to #260 from @2001LC and @suprarx7nut in the following thread give some good examples of circuit faults at or near remote harness connectors, adversely affecting AHC operation:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place
Many of the Toyota AHC fluid in black plastic 1 liter bottles, have been found to have jelled. Seems mid to early 2021 (a lot of reports out of TX), have jelled. It may have to do with plastic reaction with the fluid. Toyota witched back to the 2.5 liter tin cans, mid to late 2021.. I have 2...
forum.ih8mud.com
Relevant FSM References:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ INTRODUCTION
+ HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
+ HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE (choose your model year)
For 1998.8-, see pages IN-35 to IN38 in this sub-section for explanations and diagrams, including how probes from a multimeter are inserted for test purposes to the open back end of the connector at various ECU’s on the vehicle, without disconnecting the plug. Maybe this also is an item which should be reviewed? Note that this arrangement is different to the back end of connectors under the body etc which are sealed with a waterproof grommet.
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
+ TERMINALS OF ECU – see Page DI-218
Hope this helps!
Last edited:
Absolutely superb. #indrocruiseBack at Post #941 in this thread, I referred to a long diagnostic story posted by @YvesNL – perhaps this is the thread which should be reviewed? All of this very well-illustrated thread is worthwhile reading:
Hi From The Netherlands & AHC Issues - https://forum.ih8mud.com/threads/hi-from-the-netherlands-ahc-issues.997849/
In particular in this thread, see Post #38 and Post #44. Then Post #45 goes on to describe the follow-up to ascertain the whereabouts of the fault in the circuit which has been tested. The approach here starts with the standards for each circuit connected to the ECU as set out in FSM DIAGNOSTICS section at Page DI-218 “TERMINALS OF ECU”, as already mentioned by @uHu. This method is useful in detecting problems in a given circuit as described in the example by @YvesNL and does not necessarily focus on a particular component.
The well-illustrated Posts #253 through to #260 from @2001LC and @suprarx7nut in the following thread give some good examples of circuit faults at or near remote harness connectors, adversely affecting AHC operation:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place
Many of the Toyota AHC fluid in black plastic 1 liter bottles, have been found to have jelled. Seems mid to early 2021 (a lot of reports out of TX), have jelled. It may have to do with plastic reaction with the fluid. Toyota witched back to the 2.5 liter tin cans, mid to late 2021.. I have 2...
Relevant FSM References:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ INTRODUCTION
+ HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
+ HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE (choose your model year)
For 1998.8-, see pages IN-35 to IN38 in this sub-section for explanations and diagrams, including how probes from a multimeter are inserted for test purposes to the open back end of the connector at various ECU’s on the vehicle, without disconnecting the plug. Maybe this also is an item which should be reviewed? Note that this arrangement is different to the back end of connectors under the body etc which are sealed with a waterproof grommet.
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
+ TERMINALS OF ECU – see Page DI-218
Hope this helps!
Thank You.
I wish to thank both #uHu and #indrocruise for their determined efforts to help me find the info I’m looking for.Back at Post #941 in this thread, I referred to a long diagnostic story posted by @YvesNL – perhaps this is the thread which should be reviewed? All of this very well-illustrated thread is worthwhile reading:
Hi From The Netherlands & AHC Issues - https://forum.ih8mud.com/threads/hi-from-the-netherlands-ahc-issues.997849/
In particular in this thread, see Post #38 and Post #44. Then Post #45 goes on to describe the follow-up to ascertain the whereabouts of the fault in the circuit which has been tested. The approach here starts with the standards for each circuit connected to the ECU as set out in FSM DIAGNOSTICS section at Page DI-218 “TERMINALS OF ECU”, as already mentioned by @uHu. This method is useful in detecting problems in a given circuit as described in the example by @YvesNL and does not necessarily focus on a particular component.
The well-illustrated Posts #253 through to #260 from @2001LC and @suprarx7nut in the following thread give some good examples of circuit faults at or near remote harness connectors, adversely affecting AHC operation:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place
Many of the Toyota AHC fluid in black plastic 1 liter bottles, have been found to have jelled. Seems mid to early 2021 (a lot of reports out of TX), have jelled. It may have to do with plastic reaction with the fluid. Toyota witched back to the 2.5 liter tin cans, mid to late 2021.. I have 2...
Relevant FSM References:
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ INTRODUCTION
+ HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
+ HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE (choose your model year)
For 1998.8-, see pages IN-35 to IN38 in this sub-section for explanations and diagrams, including how probes from a multimeter are inserted for test purposes to the open back end of the connector at various ECU’s on the vehicle, without disconnecting the plug. Maybe this also is an item which should be reviewed? Note that this arrangement is different to the back end of connectors under the body etc which are sealed with a waterproof grommet.
LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
+ TERMINALS OF ECU – see Page DI-218
Hope this helps!
I acknowledge fully that #indrocruise has in part duplicated a portion of information or some of the advice #uHu had provided earlier in the week. However #indrocruise has helped uncover other critical information and a particular article that I had failed to find.
I will also openly acknowledge that I am guilty of not researching or reviewing the earlier posts in Definitive List of AHC Maintainance Items, I had focused too much of my research upon the FSM, which in itself can be tricky to navigate thoroughly.
But I will reiterate advice I was given in the past and failed to adhere to, and that was to ensure to look through all or as many previous posts as possible as invariably the answer to your querie is probably already well covered.
This was indeed the case with my querie.
I for one will give myself a rap on the knuckles and will endeavour to be a bit more diligent with my study before hassling the most excellent and overly willing contributors on this forum.
I totally acknowledge we are very privileged to have the calibre of contributors we have on this forum.
I have had a few very difficult issues to navigate through with my LC100 over the past year. There is no question that my LC100 would of been parked up by now if not for the help and guidance given on this forum. Sadly it is absolutely the case that as regards the AHC issues in particular our local Toyota dealership were more in the dark as regards repairing the system than I was myself. And as for private independent garages the Toyota AHC system is still an unknown quantity to the vast majority of them. Therefore if not for IH8MUD I am not exaggerating in saying my LC100 may well of been put off the road.
A Massive Thank you to everyone involved.
Hi #uhu and #indrocruise
Apologies for my intermittent attendance. I have been unwell and have had a couple of unplanned visits to hospital since we last connected.
As usual I am still seeking information,
I still have my last project sitting in my workshop, still seeking the proverbial AHC fault that has evaded capture all this time.
My question is simple,
There is a chart in the FSM that tells us the respective voltages we should expect from each pin on the AHC ECU.
Yes I should have started by saying I have still to test the AHC ECU Thoroughly.
My question is, each line or box on that chart start with a lettered abbreviation for the test or pin we are about to attempt to test.
Can anyone direct me to the area in the FSM that explains what all these lettered codes are?
For example,
On page DI-218 Diagnostics Active Height Control Suspension & Skyhook TEMS
TERMINALS OF ECU
The first line of the boxed code chart starts with;
Symbol (terminal No)
STP (S9-1) GND (S7-7, S9-26)
And the symbols continue down through the chart such as
REG
SS1
FRO
RC. And so on.
Can anyone direct me to the part of FSM that explains what each of these lettered codes means.
Thank you, and good to be back.
Welcome back!!
It would be good to be reminded of the symptoms being observed on your vehicle.
Usual mantra before beginning anything, revisit simple things first:
- Level ground, Front ‘cross-levelled’ to equalise RH and LH hub-to-fender distances,
- ‘Ride heights’ measured and reported at all wheels,
- LH Front and RH Front and Rear Height Control Sensors observed to be well-adjusted and in expected positions (same angular position both sides at Front, not extreme slide position at Rear),
- Age and external visual condition of Height Control Sensors observed,
- All Height Control Sensor readings reported -- expect close to zero on Techstream or other scanner,
- DTC’s noted and reported,
- If inconsistencies exist in (1) to (6) above on a 24 years old vehicle, confirm health of Height Control Sensors and circuits before proceeding further, noting as discussed elsewhere that absence of DTC’s for Sensor circuits does not provide assurance of the health of Sensor circuits.
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14466838
Meanwhile in answer to your request for information ....
The first attachment shows FSM Page DI-218.
At the top of Page DI-218, the three connectors at the ECU are shown, designated S7, S8, S9.
The column “Symbols (Terminal No.)” lists the connections to be made with a multimeter to check the Standard (STD) Voltage (V) under the “Conditions” shown.
I have not found an explicit and concise list of the abbreviations used in the first column in the table at Page DI-218. The information under the heading “Condition” gives a few clues, some are intuitive, some are a little harder to guess! However, the AHC Electrical Wiring Diagram (EWD) provides a way forward -- see details further below.
The wiring colours are self-explanatory (although there can be some differences across different vehicle models).
By way of an example, in the first line in the table at FSM Page DI-218, testing the ECU connections with the Stop-light circuit is described:
STP means “STOP” (meaning the Stop-light circuit).
GND means “Ground” (meaning electrically grounding to the chassis/body/engine of the vehicle) – this is represented by two different pins, specifically, Pin Number 7 at lower far right at Connector S7 AND Pin Number 26 at lower far left at Connector S9.
“STP (S9 – 1) – GND (S7 -7), (S9 – 26)” means check the Voltage under the prescribed conditions with the multimeter at the Stop-light pin (S9 – 1) and separately at EACH of the Ground pins (S7 -7) and (S9 – 26)
This is hard work because the ECU is tucked away under the dashboard (see Post #941 this thread) and the holding bolts need to be accessed and released to allow the ECU to swing free and so as to allow better access to the three connectors S7, S8, S9 at the ECU. The idea is for thin multimeter probes to be inserted beside where the wiring enters the plug, so as to reach the relevant terminals while the three connector plugs are still in place in the ECU and while the "Condition" requirements are followed. The attached Inspection Procedure may be helpful.
Be aware that the AHC Main Relay is attached to the ECU or it is nearby (location varies slightly on some models). If this relay is defective, then there will be no AHC or TEMS functionality at all. There is a test procedure for the AHC Main Relay in the DIAGNOSTICS section of the FSM -- look for details under C1743. The AHC Main Relay is not to be confused with the AHC Motor Relay which is located in the Junction Box in the engine bay.
The second attachment shows the AHC Electrical Wiring Diagrams (EWD) over two pages for RHD LC100 1998. These diagrams also can be found and expanded more clearly on a screen at the usual FSM on-line link:
LC100 Workshop Manual - https://lc100e.github.io/
+ Electrical Wiring Diagram
+ OVERALL ELECTRICAL WIRING DIAGRAM
+ Active Height Control Suspension
+ 1998.1 – 2000.9 (or choose other relevant year)
To assist, images of the EWD also are shown below. The overall picture would be obtained by printing and joining together these parts of this EWD.
In each of these diagrams, start at the long rectangle which represents the ECU. The same symbols or acronyms appear on the long edges of the ECU 'rectangle' as are listed at FSM Page DI-218. Use the EWD as a 'map' and backtrack from each ECU connection along the circuits to see what component and function is connected to the ECU at these points.
If an adverse test result is obtained at any of the ECU pin locations, then the next step is explore the full circuit -- components and wiring harness -- that arrive at this ECU pin AND also consider the condition of the various connectors and relays along the way.
Other helpful FSM pages at LC100 Workshop Manual - https://lc100e.github.io/ in the "Electrical Wiring Diagram" section may include those labelled
+ HOW TO USE THIS MANUAL (Explains the various symbols used on Electrical Wiring Diagrams)
+ RELAY LOCATIONS
+ ELECTRICAL WIRING ROUTING [Parts
+ ELECTRICAL WIRING ROUTING [W/W, G/P, S/P]
The Inspection Procedure may be helpful as described at
LC100 Workshop Manual - https://lc100e.github.io/
+ HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
+ HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE (explains procedure with multimeter)
Hope this helps! Glad it was a simple question
Last edited:
Hi Everyone,Welcome back!!
It would be good to be reminded of the symptoms being observed on your vehicle.
Usual mantra before beginning anything, revisit simple things first:
Note that it is possible in some circumstances for all to be healthy at the ECU but a downstream harness or connector fault may cause aberrant AHC behaviour with or without a DTC. For example, read Post #251 through to about Post #259 at this thread -- there is some good information with pictures here:
- Level ground, Front ‘cross-levelled’ to equalise RH and LH hub-to-fender distances,
- ‘Ride heights’ measured and reported at all wheels,
- LH Front and RH Front and Rear Height Control Sensors observed to be well-adjusted and in expected positions (same angular position both sides at Front, not extreme slide position at Rear),
- Age and external visual condition of Height Control Sensors observed,
- All Height Control Sensor readings reported -- expect close to zero on Techstream or other scanner,
- DTC’s noted and reported,
- If inconsistencies exist in (1) to (6) above on a 24 years old vehicle, confirm health of Height Control Sensors and circuits before proceeding further, noting as discussed elsewhere that absence of DTC’s for Sensor circuits does not provide assurance of the health of Sensor circuits.
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14466838
Meanwhile in answer to your request for information ....
The first attachment shows FSM Page DI-218.
At the top of Page DI-218, the three connectors at the ECU are shown, designated S7, S8, S9.
The column “Symbols (Terminal No.)” lists the connections to be made with a multimeter to check the Standard (STD) Voltage (V) under the “Conditions” shown.
I have not found an explicit and concise list of the abbreviations used in the first column in the table at Page DI-218. The information under the heading “Condition” gives a few clues, some are intuitive, some are a little harder to guess! However, the AHC Electrical Wiring Diagram (EWD) provides a way forward -- see details further below.
The wiring colours are self-explanatory (although there can be some differences across different vehicle models).
View attachment 3108013
By way of an example, in the first line in the table at FSM Page DI-218, testing the ECU connections with the Stop-light circuit is described:
STP means “STOP” (meaning the Stop-light circuit).
GND means “Ground” (meaning electrically grounding to the chassis/body/engine of the vehicle) – this is represented by two different pins, specifically, Pin Number 7 at lower far right at Connector S7 AND Pin Number 26 at lower far left at Connector S9.
“STP (S9 – 1) – GND (S7 -7), (S9 – 26)” means check the Voltage under the prescribed conditions with the multimeter at the Stop-light pin (S9 – 1) and separately at EACH of the Ground pins (S7 -7) and (S9 – 26)
This is hard work because the ECU is tucked away under the dashboard (see Post #941 this thread) and the holding bolts need to be accessed and released to allow the ECU to swing free and so as to allow better access to the three connectors S7, S8, S9 at the ECU. The idea is for thin multimeter probes to be inserted beside where the wiring enters the plug, so as to reach the relevant terminals while the three connector plugs are still in place in the ECU and while the "Condition" requirements are followed. The attached Inspection Procedure may be helpful.
Be aware that the AHC Main Relay is attached to the ECU or it is nearby (location varies slightly on some models). If this relay is defective, then there will be no AHC or TEMS functionality at all. There is a test procedure for the AHC Main Relay in the DIAGNOSTICS section of the FSM -- look for details under C1743. The AHC Main Relay is not to be confused with the AHC Motor Relay which is located in the Junction Box in the engine bay.
The second attachment shows the AHC Electrical Wiring Diagrams (EWD) over two pages for RHD LC100 1998. These diagrams also can be found and expanded more clearly on a screen at the usual FSM on-line link:
LC100 Workshop Manual - https://lc100e.github.io/
+ Electrical Wiring Diagram
+ OVERALL ELECTRICAL WIRING DIAGRAM
+ Active Height Control Suspension
+ 1998.1 – 2000.9 (or choose other relevant year)
To assist, images of the EWD also are shown below. The overall picture would be obtained by printing and joining together these parts of this EWD.
View attachment 3108208
View attachment 3108210
In each of these diagrams, start at the long rectangle which represents the ECU. The same symbols or acronyms appear on the long edges of the ECU 'rectangle' as are listed at FSM Page DI-218. Use the EWD as a 'map' and backtrack from each ECU connection along the circuits to see what component and function is connected to the ECU at these points.
If an adverse test result is obtained at any of the ECU pin locations, then the next step is explore the full circuit -- components and wiring harness -- that arrive at this ECU pin AND also consider the condition of the various connectors and relays along the way.
Other helpful FSM pages at LC100 Workshop Manual - https://lc100e.github.io/ in the "Electrical Wiring Diagram" section may include those labelled
+ HOW TO USE THIS MANUAL (Explains the various symbols used on Electrical Wiring Diagrams)
+ RELAY LOCATIONS
+ ELECTRICAL WIRING ROUTING [Parts
+ ELECTRICAL WIRING ROUTING [W/W, G/P, S/P]
The Inspection Procedure may be helpful as described at
LC100 Workshop Manual - https://lc100e.github.io/
+ HOW TO TROUBLESHOOT ECU CONTROLLED SYSTEMS
+ HOW TO USE THE DIAGNOSTIC CHART AND INSPECTION PROCEDURE (explains procedure with multimeter)
Hope this helps! Glad it was a simple question
im working on a friends LC100 2007 Facelift Model.
He is having a serious problem with his AHC system. The AHC Off light is flashing steadily, and the Height selector is stuck at Lo.
The AHC is not working with the LC sitting permanently at Lo.
The AHC was working fine until a front Hydraulic Shock absorber burst. It was replaced but they couldn't get the AHC to go again.
l have carried out the DTC procedure and the Active Test / Restart procedure.
The DTC"s are as follow, 31 32 33 34 36 43 all of which are related to the AHC and AHC ECU problem.
Having checked status of all fuses and the AHC relays, One in Fuse box and the other on the AHC ECU Box itself. All fuses are fine, and the relays are working perfectly.
l have been testing the AHC ECU with a multimeter.
One really odd reading is that when i test for voltage on {S9. -- 13} and {S7 -- 7} The Multimeter reads 12volt for 1 second and then gradually drops to 0 Volt until l switch off the ignition and then switch it on again. Then it repeats the same behaviour. Has any of the Forum members experienced this before?
Could the ECU be damaged or faulty?
Thank You.
Last time that happened to us (working on a friend's truck) we had left the tailgate open! Just check to make sure every door is closed!
Thank you Classy Jalopy.
Can you please confirm when you say “The last time that happened——“
Are you referring to the 12v reading slowly stepping down to 0v on the multimeter?
All doors were closed and boot closed but I will definitely check all the open-close “switches” to be sure they are functional.
NO just the OFF light flashing!
Hi Indrocruise
Great to connect again and thank you for your detailed reply.
Thanks to your detailed descriptions and instructions I have slowly learned to go through all the steps as you have listed, pre any DTC Testing.
With all steps covered and all doors/boot closed have you ever experienced or heard of the multimeter behaviour I was having?
In this I mean, when I put fine probs
Hi Indrocruise
Great to be in contact again.
Due entirely to your detailed descriptions and instructions I have slowly learned to adhere strictly to the list of Pre Diagnosis steps as you have outlined in your post.
Taking that I have done so and all doors and boot are closed firmly, have you ever experienced or heard of such like multimeter behaviour as I have described. Meaning that when I was testing the ignition input voltage to the AHC ECU (S9–13) and (S7–7)the meter read 12v but slowly dropped step by step down to 0v. The only way I could get it to read 12v again was to turn the ignition off again and then on again. In each instance it did the same thing starting at 12v and dropped slowly to 0v.
Cheers
Appreciate you confirming this.
Thank you.
Absolutely brilliant pieces of engineering. I am probably mad but I’m trying to learn the ins and outs of diagnosing and fixing the AHC system on these vehicles. We have no one to go to as regards fault finding or repair of the AHC, and that’s including the Toyota dealership. They simply have not got a clue as to the Maintainance or repair of this system.
Appreciate you confirming this.
Thank you.
Absolutely brilliant pieces of engineering. I am probably mad but I’m trying to learn the ins and outs of diagnosing and fixing the AHC system on these vehicles. We have no one to go to as regards fault finding or repair of the AHC, and that’s including the Toyota dealership. They simply have not got a clue as to the Maintainance or repair of this system.
