AHC 'OFF' Blinking

[adyargarage]

hi everybody, i got 1 problem about AHC system. 'OFF' indicator still blinking and cannot change to mode N,H and L.
when i check use scan tool found 2 DTC:-
1) C1762 Abnormall oil pressure for pump
2)C1751 Continuous current to compressor motor

I already check the ahc fluid level - ok
Check for leaking in pipe lines and accumulator - ok
based on your experience wheres the trouble area and how procedure to start the checking..

 

[jOnathN]

A) Not enough info be really helpful
B) Art ('agaisin' on this board) is probably your best bet for advice as he has done a lot more digging on the codes.

So, that said, two things come to mind:
1) there is a pressure sensor that shuts off the pump at the right psi. That may have gone bad. It is located on the pump assembly on the PS firewall.
Theory - the pump is ok and raising pressure but pressure switch is bad so pump keeps running. The ECU sees no pressure (because of the bad sensor) after the max run period and shuts off the pump to prevent damage (the pump is not rated for continuous duty). ECU sets the two codes.
2) your pump could be bad...if it is really worn then it may be spinning but not able to raise the system to operating pressure before max run time is reached. This could also happen if you lost a lot of fluid somewhere e.g. the main accumulator is empty. You said the level looks fine though so probably not that.
Theory - pump is worn out. It raises pressure but not high enough to trip the sensor so it keeps running until the ECU notices, shuts it off, and sets the two codes.

Also check your fuses of course.

How old is the truck, how many miles, and how has the AHC performed over the last few months? Is the ride harsh, smooth, bouncy, ...? Does it frequently adjust at stoplights and so forth or only every once in a while? Do you ever adjust the ride damping between comfort and sport and (if you do) is there a noticeable difference or are all settings pretty much the same? Anything else come to mind?

 

[agaisin]

Fortunately I don't have much experience with the AHC specific codes and how to interpret - there is plenty of info in the FSM but apparently it can sometimes be misleading.

uHu seems to have a lot of experience there so maybe he can chime in and I'm sure others have dug deeper into the nitty gritties.

Here's what the FSM says about diagnosing both those DTCs, maybe it'll help:
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Regarding C1762/62,
DTC Detecting Condition is
1) While the motor relay is in operation, the condition that the fluid pressure is less than .5 MPa continued for .6 seconds.
2) When the pump motor is in delivering condition, the delivery portion does not change and the fluid pressure change is small.
Trouble Areas are: AHC Pump and Motor, Fluid Pressure Sensor, AHC Motor Relay, or Fluid is Empty.
Fail Safe Function:
If the DTC C1762/62 is detected, the height control is prohibited after adjusting the vehicle height to the standard height in case that the height is higher than the standard or to the lowest wheel of the 4 wheels in case that the height is lower than the standard.
See the FSM for more details but here's a summary of the inspection procedure: check fluid of the reservoir tank, check operation of AHC pump & motor, bleed air of AHC & AVS hydraulic system, Check AHC motor relay, check for open and short circuit in harness and connector b/w fluid pressure sensor and suspension control ECU, check fluid pressure sensor. Each of those checks has numerous detailed steps so you really need the FSM for more detail.

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Regarding C1751/51, the Circuit Description is "In case that the height control has not consisted in spite of performing the raise control for a certain period of time, the ECU interrupts the height control."
The DTC Detecting condition is "When the rise control completion condition has not consisted in spite of turning on electricity to the relay for the following period of time LO to N 85 Seconds, N to Hi 100 seconds."
Trouble Areas are: AHC pump & motor, AHC pump & motor circuit, AHC motor relay, height control sensor link comes off, Fluid Leakage from the fluid line or each solenoid valve, Fluid clog in the fluid line or each solenoid valve, Torsion bar spring.
Fail Safe Function: "If trouble occurs, the height control is prohibited after adjusting the vehicle to the standard height in case that the height is higher than the standard or to the lowest wheel of the 4 wheels in case that the height is lower than the standard."
The inspection procedure has you check the fluid level, check fluid leakage, check that the heigh control sensor link has not come off, check fluid delivery pressure of the AHC pump motor, check the AHC motor relay, and check for open and short circuit in harness and connector between AHC pump motor and suspension control ECU, AHC motor relay and battery.
------------------------

So - you say you checked fluid level and it's ok. I'll take your word for that. You say you checked for leaking ok.

Take a look at the other trouble areas for both DTC's as quoted above. That should give you plenty to look at and hopefully eliminate/isolate.

Also interested in your answers to jOnathN's questions - basically more info on your vehicle's history and symptoms leading up to this point.

 

[agaisin]

Here's another relevant thread where two posters (darkd and Joe422) fixed their issue by replacing the pump sub assembly:
https://forum.ih8mud.com/100-series-cruisers/285893-lx470-ahc-problems.html
The original poster in that thread (fish933) also had this continuation thread https://forum.ih8mud.com/100-series-cruisers/294129-lx470ahc-troubles-update.html#post4614877 but never says whether he fixed the problem or not. He definitely had the C1751 and C1762 though.

Here's Joe422's post: https://forum.ih8mud.com/100-series-cruisers/287320-finally-fixed-my-ahc-changed-pump.html

BonS seems to have solved his problems of not raising with a new pump sub assembly: https://forum.ih8mud.com/100-series-cruisers/206991-my-lx470-ahc-woes-id-love-your-help.html

 

[CBeckFJ]

Resurecting this thread. My LX started blinking the "off" light recently, but it's lifted 2.5" on foam cell pros. Not sure what could be throwing the code, maybe level sensors?

 

[jLB]

Resurecting this thread. My LX started blinking the "off" light recently, but it's lifted 2.5" on foam cell pros. Not sure what could be throwing the code, maybe level sensors?

All I did was disconnect the 50A fuse under the hood. AHC diagram on the dash is stuck in high, but no other lights appear.

Pull the bottom two connectors on the AHC ECU?

 

[CBeckFJ]

Pull the bottom two connectors on the AHC ECU?

Haven't tried that yet, I'll take a peek tomorrow. Thanks!