AHC active test

[Chris T]

So having completed a replacement burst pipe I've now run into another problem the car refuses to pick itself back up.
I know from running tech stream that the rear ride height sensor is throwing a DTC I plan to replace it at some point but getting the car drivable was then goal.
No problem I thought let me do an active test and see if I can't force the front end back up to ride height.
From my understanding you should be able to jump the TS and E1 pins and then using the controller raise the front and rear independently of each other.
Unless I'm an idiot I'm getting sweet nothing, no pump activity at all.

So the question is does the failed ride height sensor prevent the active test from running the pump?

 

[TXLXAG]

I don’t know for sure the relationship between the ride height sensor and the operation, but I just had the active test also not work.
I replaced my globes about 6 months ago, and did not bleed enough. I had a decent amount of air in the system and it started the pogo again in the front. I bled the system, all 4 globes and the center height accumulator. Went ok for 2 raises and then the back end fell to the bumpstops.
It took me 2 days of repeatedly trying active test(never worked), clearing codes, applying 12v direct from the battery, and clearing codes before it finally worked.
I rocked the car back and forth after clearing codes and starting the engine and noticed the “abnormal pressure” DTC didn’t come back on as fast when I kept rocking it back and forth. I jacked up the back end by the pumpkin until tires were about 2-3” in the air, started the engine and rocked it repeatedly, and it eventually caught and lifted. I bled the system and cycled it L-N-H probably 10 times after that. So far it’s been working great.

 

[IndroCruise]

So the question is does the failed ride height sensor prevent the active test from running the pump?

Yes -- see detailed responses to @Chris T in other threads. Where a Height Control Sensor Circuit failure (Sensor or Connector or Harness) causes "Fail Safe Function" to be initiated by the Suspension Electronic Control Unit (ECU), this will not be over-ridden by Active Test.

Conversely, if Active Test will not work, it is being prohibited by a defined fault somewhere in the AHC/TEMS systems.

The task then is to find the fault that is preventing the Active Test operation.

 

[IndroCruise]

I don’t know for sure the relationship between the ride height sensor and the operation, but I just had the active test also not work.
I replaced my globes about 6 months ago, and did not bleed enough. I had a decent amount of air in the system and it started the pogo again in the front. I bled the system, all 4 globes and the center height accumulator. Went ok for 2 raises and then the back end fell to the bumpstops.
It took me 2 days of repeatedly trying active test(never worked), clearing codes, applying 12v direct from the battery, and clearing codes before it finally worked.
I rocked the car back and forth after clearing codes and starting the engine and noticed the “abnormal pressure” DTC didn’t come back on as fast when I kept rocking it back and forth. I jacked up the back end by the pumpkin until tires were about 2-3” in the air, started the engine and rocked it repeatedly, and it eventually caught and lifted. I bled the system and cycled it L-N-H probably 10 times after that. So far it’s been working great.

There can be various causes of the "Fluid Pressure Abnormality" Diagnostic Trouble Code (DTC) C1762. By far the most is common cause is when there are large quantities of air in the AHC/TEMS system. Other causes can include partial blockages of the strainers inside the AHC Pump or incorrect operation of the Return Valve.`

The point is that the response time of DTC C1762 is very quick -- about 0.6 seconds according to the FSM extract immediately below -- at which time the Suspension ECU initiates the "Fail Safe Function" defined below. This prohibits the Height Control function, meaning the ECU prevents operation of the AHC Pump, and, meaning the ECU may cause the vehicle to drop to the level of the lowest wheel.

The fix procdedure described on the second page of the full FSM extract for DTC C1762 attached below is similar to the Active Test, except that the instruction is to start to bleed with the pump motor operating. This would mean that the ECU causes opening of the Levelling Valves in the Control Valve Assembly to allow AHC Fluid to pass to the open bleeding screw(s).

However, experience shows that this procedure does not always work and the defined "Fail Safe Function" repeatedly stops the AHC Pump after ~0.6 seconds.

When this happens, the repetitive effort described by @TXLXAG in Post #2 is the practical workaround.

 

[Chris T]

Thank you for the repeated help, I feel like I'm loosing it.
Am I being a dunce?
Worked my way through steps 1 and 2 of DI-9 all fine no issues got to step 3 "bleed air out of ahc and tems system"
Looking at the DLC3 port on the top row working left to right the TS pin should be the third along? However there's no pin in the third position from the left. What am I missing here?

Skipping past that step and onto step 4 I get 69ohms over the relay, is that to high?
I currently do have a good way to apply battery power to the relay so unsure if it's operating correctly when power is applied.

Step 5 fluid pressure sensor.
How do I go about this with sensor on or off? Or do I need to be able to probe the backside? Does that mean revealing a section of the conductors.

 

[Malleus]

It's late, and I may be sleep–typing, but aren't you supposed to use the DLC1 terminal, on the engine side of the firewall?

 

[Malleus]

DLC1 Pinout guide:

 

[Malleus]

DLC3 Pinout guide:

 

[Chris T]

It's late, and I may be sleep–typing, but aren't you supposed to use the DLC1 terminal, on the engine side of the firewall?

Most tests do. However this particular test from the FSM suggested by @IndroCruise uses DLC3 hence the ask.

 

[Malleus]

Then he means pins 4 (chassis ground) & 14 (CANbus)

 

[IndroCruise]

Most tests do. However this particular test from the DLC3 suggested by @IndroCruise uses DLC1 hence the ask.

View attachment 3986085

The DLC3 under the dashboard of 2006 LC100 RHD with AHC and 1HD-FTE vehicle delivered in Australia is as shown below. It appears to be in order and is suitable for test connections -- although I have had so much trouble achieving a stable connection to the 'unofficial' versions of Techstream that I gave up and resorted to other kinds of scanners capable of reading the Suspension Electronic Control Unit (ECU), as needed for AHC pressures or other diagnosis from time to time, using DLC3.

For convenience and relevant test purposes, I prefer to bridge between Ts and E1 at DLC1 in the engine bay, knowing that this provides equivalent ECU connections as the FSM bridging between Ts and CG at DLC3 as noted long ago by @PADDO at
AHC - is my mech fleecing me? - https://forum.ih8mud.com/threads/ahc-is-my-mech-fleecing-me.928828/#post-10372748 . Testing using DLC1 in this way also appears in some versions of the Factory Service Manuals, as attached. This is consistent with the endorsement in this thread by @Malleus.

The AHC Motor Relay should be removed from Junction Box in Engine Bay and tested per instructions contained in Test Procedure attached to Post #4 -- not to be confused with the AHC Main Relay which is located under the dashboard with the Suspension ECU.

FSM reference value for continuity at AHC Motor Relay between terminals 3 and 4 is 62 ohms -- unable to say whether 69 ohms is too high.

Suggest continue on with the next steps in the procedure for AHC Motor Relay:

• Apply battery voltage (12 volts) between terminals 3 and 4 (follow polarity shown in the diagram for the test procedure) ,
• Check continuity between terminals 1 and 2 -- while voltage is still applied between terminals 3 and 4, with correct polarity.

While I try to avoid guesswork and prefer evidence-based diagnosis, the descriptions in your various posts in the thread
AHC Error code S307-82 - https://forum.ih8mud.com/threads/ahc-error-code-s307-82.1367411/#post-16055686
do suggest lack of power in the AHC/TEMS systems. This leads to deep suspicions about the AHC Main Relay under the dashboard. If the AHC Main Relay is faulty, then none of the AHC/TEMS functions will work and there may be no specific DTC's. As mentioned in my reply to that thread, it is also recommended that the AHC Main Relay be removed and tested per the relevant procedure, as part of the test sequence suggested in that reply. Noting the previous issue with the Rear Height Control Sensor circuit, this remains suspicious until testing or replacement -- cleaning/inspection is insufficient.

The different test procedures for the AHC Motor Relay and the AHC Main Relay and the AHC Pressure Sensor and the AHC Height Control Sensors are attached. These were downloaded from the previously provided link to to the actual Toyota on-line Factory Service Manual -- HOME | LC100 Factory Service Manual - https://lc100e.github.io/

Hope this helps!

 

[Malleus]

This is from the 2003 LX470 (USDM) service manual [the UK service manual may be different]:

and so on. I'd be very leery of shorting the CANbus terminal to ground (using the DLC3 connector), if you do not know what you're doing. The CANbus is a network; every electrical system on the truck is connected to it, and every node has to work.

This is the downside of the CANbus architecture for automotive use. For industrial use, it's great, becuase when you have a fault, everything shuts down, and you know there's a problem. No one gets hurt and there can't be any snakes in the woodpile, waiting to bite you when you're not looking. I'd personally rather not have my truck wired that way, but no one asked me.

 

[IndroCruise]

This is from the 2003 LX470 (USDM) service manual [the UK service manual may be different]:
View attachment 3986394
View attachment 3986396
View attachment 3986399View attachment 3986401
View attachment 3986403
and so on. I'd be very leery of shorting the CANbus terminal to ground (using the DLC3 connector), if you do not know what you're doing. The CANbus is a network; every electrical system on the truck is connected to it, and every node has to work.

This is the downside of the CANbus architecture for automotive use. For industrial use, it's great, becuase when you have a fault, everything shuts down, and you know there's a problem. No one gets hurt and there can't be any snakes in the woodpile, waiting to bite you when you're not looking. I'd personally rather not have my truck wired that way, but no one asked me.

Thanks @Malleus -- that's very useful and has given me cause to do a bit of research and strenthen my hazy knowledge of automotive CANbus ('CAN' being Controller Area Network and 'bus' being the two-wire shared connections to multiple components around the vehicle -- as I understand or misunderstand it).

Your images at Post #12 are like-for-like, page-by-page, with the extract I have offered previously (attached again for clarification), as posted on this Forum long ago by @PADDO -- and which I believe he also extracted from the 2003 LX470 Factory Service Manual for the US Domestic Market (USDM), although @PADDO also had Australian connections as denoted by his avatar.

To that extent, all are "on the same page" concerning connections and procedures at DLC1 -- and which I prefer.

Then going to the online version of the LC100 Factory Service Manual which is published with the header TOYOTA OVERSEAS CUSTOMER SERVICE TECHNICAL DIVISION -- found at HOME | LC100 Factory Service Manual - https://lc100e.github.io/ -- and used by many IH8MUD Members around the world, the same test procedures are found, but using specified connections at DLC3, rather than DLC1. Two examples follow below:

-- using Tc to CG for Pre-check - Diagnosis System:

-- using Ts to CG for Height Control Operation Test (Active Test):

Just wondering if @Malleus (or anyone else) can throw any more light on the equivalence or otherwise of the different connections using DLC 1 versus DLC3 for test procedures which otherwise are exactly the same???