AHC woes

[Africaster]

Wish there was something more definitive we could do, but without being on site, we’re throwing darts in the dark. To lower your reliance on those dodgy mechanics, probably time to get your own TechStream, roll up your sleeves and using Google/YT and the likes, start at one end and systematically work through the entire system. Good luck.

 

[AtinLango]

Wish there was something more definitive we could do, but without being on site, we’re throwing darts in the dark. To lower your reliance on those dodgy mechanics, probably time to get your own TechStream, roll up your sleeves and using Google/YT and the likes, start at one end and systematically work through the entire system. Good luck.

I agree. That is the ultimate solution. Mechanics here are of no help in this.

The mechanic i hvue refered to before (the one who changed the shocks/globes a few months ago, and has been working on my AHC since then) is a former Toyota worker. I was referred to him by someone who owns my type of car. Prior to this, i was servicing the AHC (fluid changes) by getting a mechanic and giving instructions. I had five years of absolutely no AHC issues.

This mechanic seems to have an issue because i have had three or four incdents of AHC stuck in L in the short time i have been with him. He always refuses to bleed the system after fitting back the pump or globe. And once i pay him, he disappears and refuses to pick calls.

 

[AtinLango]

For clarity, i have not yet bought my own Techstream. I just got another mechanic nearby who has Techstream and can use it effectively (unlike others who were not even able to get the DTC). I wil definitely buy my own as soon as i can. For now, i can easily reach the mechanic with Techstream if i need to.

 

[suprarx7nut]

You need to bleed. 10 turns might be fine. You have to read pressures from Techstream after you get it working to know what assignment is needed.

The system has air. You have to bleed. You'll want to use the active test to force the pump to run if you can. Just recently @BullElk ran into a bad pump that needed new o-rings. That might be what you're seeing now.

 

[AtinLango]

You need to bleed. 10 turns might be fine. You have to read pressures from Techstream after you get it working to know what assignment is needed.

The system has air. You have to bleed. You'll want to use the active test to force the pump to run if you can. Just recently @BullElk ran into a bad pump that needed new o-rings. That might be what you're seeing now.

Thank you for the insights.

 

[AtinLango]

I have now got another mechanic who says he knows AHC system. I will meet him tomorow. If he really knows, I will be keen to learn bits and pieces from him so that I am able to survive on my own.

 

[J1000]

It's easy to bleed the accumulator and globes. No need to remove them just open the bleed screw with the wheels on the ground. The weight of the vehicle with push out the air, not the vehicle will drop down slightly. The system is self bleeding to an extent but needs to have most of the air out first.

 

[AtinLango]

It's easy to bleed the accumulator and globes. No need to remove them just open the bleed screw with the wheels on the ground. The weight of the vehicle with push out the air, not the vehicle will drop down slightly. The system is self bleeding to an extent but needs to have most of the air out first.

I know, but this is not possible in the current state of the vehicle - stuck in L with no pressure.

 

[J1000]

I know, but this is not possible in the current state of the vehicle - stuck in L with no pressure.

There may still be some residual pressure and if you bleed out the air then it may start working again. Can't hurt to try. You should reach the AHC ABCs and figure it out yourself since it seems hard to find good mechanics in your area.

 

[BullElk]

You do need to bleed it but there were abnormal pressure issues before mechanic opened it up and possibly let air in it.

 

[AtinLango]

I tried bleeding accumulator and globes, but there is no pressure.

Also failed to bleed using active test (both manual and using Techstream).

Connected DC from battery to pump. The pump is running.

Finally found fuses for AHC-IG and AHC B inside passenger side. Both fuses are okay.

Next plan is to take pump apart. For this, i have got someone who can do it for me tomorrow. If i try with my limited knowledge, i will mess everything up.

 

[uHu]

Atin, before doing any major job, like disassembling the pump, you should check the status of the signals from the height sensors.
This can be read in TechStream (post a screenshot here). The height sensors are the most common source of problems like you describe, and that can be either a worn out sensor, corrosion, cabling or linkage. If the signals are wrong, the AHC ECU will not do anything, and will not open any valves to give you pressure. E.g. if the left and right front sensors are reporting values which are far apart, the ECU will "shut down". If the car is in position Low, and one of the sensors show Hi, the ECU will not do anything. As the car sits at Lo, all 3 sensors should show somewhere between -20 and -70 mm. If they don't, the ECU will not do anything (because one value is far out (approx. values)). If the signal from one sensor is unstable (because of wear, corrosion inside, or loose linkage) you can get an AHC that sometimes will work and sometimes not.

Also a simple thing like a faulty door sensor/switch can inhibit the AHC. Again: check TechStream.

If you read through the major AHC threads on this forum, you would know much better where to start looking.
Without TechStream* and an understanding of the AHC system you will not get anywhere. The fault codes of the AHC are not sufficient to find the problem, and are often more confusing than clarifying (this is one of the major drawbacks of the AHC on the 100). Problems with the height sensors are generally not reported as faults at all.

*: Without TechStream, it is possible to repair the system by use of a multimeter, pressure gauge, the FSM, blink codes, and a good understanding of electronics and the AHC system.

 

[AtinLango]

Atin, before doing any major job, like disassembling the pump, you should check the status of the signals from the height sensors.
This can be read in TechStream (post a screenshot here). The height sensors are the most common source of problems like you describe, and that can be either a worn out sensor, corrosion, cabling or linkage. If the signals are wrong, the AHC ECU will not do anything, and will not open any valves to give you pressure. E.g. if the left and right front sensors are reporting values which are far apart, the ECU will "shut down". If the car is in position Low, and one of the sensors show Hi, the ECU will not do anything. As the car sits at Lo, all 3 sensors should show somewhere between -20 and -70 mm. If they don't, the ECU will not do anything. If the signal from one sensor is unstable (because of wear, corrosion inside, or loose linkage) you can get an AHC that sometimes will work and sometimes not.

If you read through the major AHC threads on this forum, you would know much better where to start looking.
Without TechStream* and an understanding of the AHC system you will not get anywhere. The fault codes of the AHC are not sufficient to find the problem, and are often more confusing than clarifying (this is one of the major drawbacks of the AHC on the 100). Problems with the height sensors are generally not reported as faults at all.

*Without TechStream, it is possible to repair the system by use of a multimeter, pressure gauge, the FSM, blink codes, and a good understanding of electronics and the AHC system.

Very good insights. Many thanks.

I can only get the sensor signals when i ask for Techstream from the mechanic. The earliest possible is tomorriw.

The good thing is that i have safely parked the car for now.

 

[AtinLango]

Atin, before doing any major job, like disassembling the pump, you should check the status of the signals from the height sensors.
This can be read in TechStream (post a screenshot here). The height sensors are the most common source of problems like you describe, and that can be either a worn out sensor, corrosion, cabling or linkage. If the signals are wrong, the AHC ECU will not do anything, and will not open any valves to give you pressure. E.g. if the left and right front sensors are reporting values which are far apart, the ECU will "shut down". If the car is in position Low, and one of the sensors show Hi, the ECU will not do anything. As the car sits at Lo, all 3 sensors should show somewhere between -20 and -70 mm. If they don't, the ECU will not do anything. If the signal from one sensor is unstable (because of wear, corrosion inside, or loose linkage) you can get an AHC that sometimes will work and sometimes not.

Also a simple thing like a faulty door sensor/switch can inhibit the AHC. Again: check TechStream.

If you read through the major AHC threads on this forum, you would know much better where to start looking.
Without TechStream* and an understanding of the AHC system you will not get anywhere. The fault codes of the AHC are not sufficient to find the problem, and are often more confusing than clarifying (this is one of the major drawbacks of the AHC on the 100). Problems with the height sensors are generally not reported as faults at all.

*Without TechStream, it is possible to repair the system by use of a multimeter, pressure gauge, the FSM, blink codes, and a good understanding of electronics and the AHC system.

I have had some reflections after reading this reply.

There is one significant thing that changed after replacimg shocks and globes a few months ago.

The rear of the car became too high, so the mechanic replaced the rear sensor linkage with a different type which can slide further in order to lower the rear. I have kept the original linkage.

Note that i have had issues with AHC only after that work by the mechanic. For five years before, i never had a single AHC issue.

This has left me thinking whether the change in rear linkage could have a role in my woes. Just thinking.

 

[Africaster]

I have had some reflections after reading this reply.

There is one significant thing that changed after replacimg shocks and globes a few months ago.

The rear of the car became too high, so the mechanic replaced the rear sensor linkage with a different type which can slide further in order to lower the rear. I have kept the original linkage.

Note that i have had issues with AHC only after that work by the mechanic. For five years before, i never had a single AHC issue.

This has left me thinking whether the change in rear linkage could have a role in my woes. Just thinking.

That’s where the interaction between torsion bars and hight sensors becomes crucial using TechStream … using “a different type” of sensor is not helping … “replacing shocks and globes a few months ago” has now also become a potential contributor … new? OEM? Installer same chap who doesn’t believe in bleeding?

 

[AtinLango]

Waiting to get Techstream tomorrow and take readings of sensors.

Meanwhile, i have remembered that yesterday when we toolk the first DTC using Techstream, we got the attached. After clearing the codes, only 1762 remained.

Is this image of any significance? Could it actually mean there were issues with the right front sensor?

 

[BullElk]

All of the other codes are probably a result of the abnormal fluid pressure. I had other codes as well to begin with but then only 1762. Again I say, If you're going to take the pump apart again, change the O-rings....and techstream cannot do it for you nor tell you if it is the issue.

 

[uHu]

Waiting to get Techstream tomorrow and take readings of sensors.

Meanwhile, i have remembered that yesterday when we toolk the first DTC using Techstream, we got the attached. After clearing the codes, only 1762 remained.

Is this image of any significance? Could it actually mean there were issues with the right front sensor?

View attachment 3456592

Looks like you have fault with both front sensors. Looking at the screen for the AHC values would give more info.


BTW, 5 years without an AHC issue is not good. That means your pressures were too high, as they do go up every year. You need to compensate, not every year though, depending on miles, by adjusting Torsion bars and changing rear coils, e.g.

 

[Wilsil]

Very good insights. Many thanks.

I can only get the sensor signals when i ask for Techstream from the mechanic. The earliest possible is tomorriw.

The good thing is that i have safely parked the car for now.

And that's why it is best to have your own version of Techstream.
Cheap on ebay. All you need is a laptop running XP in VirtualMode.

 

[Escape Artist]

Before you take anything apart ... I just want to point out that there is a weight load limit on the AHC to move from N to H or from L to N. You put 720 Lbs or 326Kgs of fuel in the back of the truck and the overall weight capacity of the truck is 1200 lbs total or 544Kgs and that includes the driver, passengers, bumpers, etc etc. You were likely just over the limit and the system will not raise the truck. Some guys put stock 100 series coil springs in the rear to compensate for this and then re adjust the AHC pressures etc. Adjusting the torsion bars will not help in this case as the load was in the rear of the truck. Keep in mind if your truck is a little older and the rear springs a little tired that 1200 lbs load limit is going to be more like 900 lbs. Also to note, that if the truck is at more than a 10 degree tilt the AHC will not adjust the ride height either. And if you foot is on the brake for too long like descending a steep hill and then you want to go into H mode, it will not raise up until you re apply the brake.