AHC help needed

[Kalino_74]

making sure I read this correct: "For some reason now my passenger side TB bolt will not turn CW or C. My truck is spotless underneath but I did spray with WD 40 for good measure. The driver side turns both directions with ease. I've tried putting the truck in H mode and I even lifted the front tires off the ground without success."

you are turning the TB bolt while the wheels are up in the air, correct?

Craaazy. I soaked the bolt in WD40 for a few days and even bought a spare just in case it snapped on me but I did get it moving. It’s still very hard to turn but it is moving. I did try lifting the front tires off the ground before soaking for days and it still didn’t want to budge. Thank for your input buddy.

 

[craaaazzy]

No prob. Just wanted to make sure that whenever you are adjusting the TB, front wheels are off the ground

 

[PADDO]

Thank you Paddo for the info on the pump/ reservoir that give me a greater understanding of the pump.

So this morning I got my front pressure set to 6.7 and the truck still is very stiff up front. When I push down on the front bumper at the corners there is no compressing the shocks.

I did the 16 step damper test again and when I can easily compress the shocks by pushing down the corner of each bumper. It also drives really smooth in the first say 8 steps.

Questions.

1) While the 16 step is being performed does it bypass the certain parts of the AHC computer? It seems like whatever sensor tells the computer how much damping to send to the front shocks is faulty, but no codes. Could the AHC cpu be bad?

2) If everything seems to be working fine during the 16 step test does this mean all the individual components are working fine?

When you put it into the 16 step mode the AHC ECU is in a “not normal” test mode. It’s very unlikely your ECU is defective - if it’s sending valid output pulsed signals to the front channel stepper motors in stationary test mode ( soft to hard damping test) but something seems wrong in normal dynamic driving (not test) then you’d need to consider if the dynamic inputs like front wheel speed and front height sensor feedback are valid. There’s a signal input test you can perform. Do you have the FSM? and I’m sure I’ve posted it up in .pdf a few times. If the front damping seems too hard while driving, but good in stationary test, you might have something like bad height feedback causing the front to raise, +1 inch in front height ~2.2MPa pressure increase for example and that will ruin damping. Remote diagnosis has its challenges not being able to watch Techstream feedback values etc and feel what’s going on.
And for adjusting your TBs, FSM says to do it on flat level ground which has worked for me and many others. There should be no need to lift the front wheels off the ground. The most torque I’ve ever had to put in to turn them is less than 70ft lbs. For non AHC vehicles with their heavier TBs it’s a different story.

 

[Kalino_74]

I do not have a FSM but I will do a search to try and come up with the input signal test like you mentioned. Can you tell me what sensor communicates with the stepper motors that control dampning. I’m trying to get a better understanding of how each component works and how they function with each other.

I really appreciate your help with this.

 

[Kalino_74]

Paddo, I did notice on my scan today my steering wheel sensor showed 1150 degrees. I have a 2002 and I read somewhere that out of spec steering angles can effect calving to the front shocks to prevent body roll. Can I reset this sensor with Techstream? I don’t want to get my hopes up but this could be my problem.

 

[PADDO]

I do not have a FSM but I will do a search to try and come up with the input signal test like you mentioned. Can you tell me what sensor communicates with the stepper motors that control dampning. I’m trying to get a better understanding of how each component works and how they function with each other.

I really appreciate your help with this.

The AHC ECU outputs pulsed signals to the front and rear dampening cct stepper motors, so no sensors are connected directly to the damping stepper motor assemblies. The ECU uses wheel speed and height sensor values that represent the upper control arm to frame displacement, braking for anti dive, acceleration for anti squat, cdl lock, L range, damping mode selection and steering angle. It uses a few others like oil temperature, generator voltage (so it knows the engine is running) but the ones listed are for self leveling and adaptive suspension. Nothing cool like accelerometer inputs for this generation of suspension. That's for the 570s.

For the steering angle error you've mentioned are you referring to the value displayed in the AHC data list? that should be zero with the wheels pointed straight ahead for the system to work as designed. The easiest way (only way I've found and I've looked pretty hard) to reset that is to park with your wheels straight ahead and pull the main battery neg cable for 15 minutes to clear/reset memory, or pull both pos and neg cables and short them together for a bit (just the vehicle cable, don't short the battery!). This is a good time to clean the throttle body and MAF. On reconnecting you might have a rough idle until it warms up but your AHC steering angle should be zero or very close to zero. If you have the time and inclination go for a drive before doing this reset with techstream running and monitor the two fields FG (front Gate) and RG (rear Gate) as they are the two solenoids that normally hydraulically connect the left and right shock actuators. If one or both are ON when driving straight then your left/right sides are isolated which will definitely stiffen the ride and thats not supposed to happen. They are suppose to isolate only when cornering with a bit of speed and steering wheel angle, when enhanced roll stability and stiffness is desired.

 

[Kalino_74]

I'm about to take the truck for a test drive with the techstream hooked up. I'm sorry for my ignorance but two fields FG and RG is that the same as SLFG and SLRG on techstream? Also my steering angle in AHC data list shows to only be off 40 degrees but in the ABS/VSC/TRAC data list it shows 1150 degrees. I'm not sure what this means.

 

[Kalino_74]

I did a test run with the techstream hooked up and monitored the SLFG and the SLRG. They both remained off while driving in a straight line. I was able to get the SLFG to turn ON while doing a large donut but I could not get the SLRG to turn ON, I'm not sure if that significant or not. I did the reset per your instructions and I'm still getting 1150 degrees in the ABS/VSC/TRAC section. Is this a false reading of sorts?

 

[PADDO]

I did a test run with the techstream hooked up and monitored the SLFG and the SLRG. They both remained off while driving in a straight line. I was able to get the SLFG to turn ON while doing a large donut but I could not get the SLRG to turn ON, I'm not sure if that significant or not. I did the reset per your instructions and I'm still getting 1150 degrees in the ABS/VSC/TRAC section. Is this a false reading of sorts?

That 1150 value in the ABS/VSC/TRAC does not affect damping (no input to the AHC ECU) and can be reset with a zero point calibration/memory clear, followed by a memory reinitialization. There's a good TSB that clarifies the full FSM procedure which is a bit vague and it does mention that that 1150 value can be spurious. I'll find it for you. I've had the same 1150 value coming up in the ABS data fields with no ill affect on damping and I've tried to correlate that value with VGRS (you don't have) and the AHC/AVS steering angle value displayed in the AHC data field and wasn't able to find any cause/effect. The operation of your SLFG and SLRG (I dropped the SL for solenoid previously) sounds normal. You've almost got to drive like you stole it to get both to operate.
What are your front and rear step values when driving at 30/40 mph on a smooth road with damping select switch starting at 1 and then stepping up to 4. My normal, smooth road values at those speeds would range in the 3s to 5s (pos 1) front and up to 12s in position 4.

 

[Kalino_74]

Please don't worry about the finding the info on resetting the steering angle, you've already have gone out of your way to help me. I'm going to hook up the techstream and go for a test run and I will report back with my findings.

 

[Kalino_74]

So here are my numbers from my quick test drive going between 30-38mph

I wasn't sure what was 1 on the damping switch so I'm going with "1" being sport mode.

1=10 both sides even
2=6 both sides even
3=2&3
4=1

I hope this helps.

 

[PADDO]

The convention for the damping comfort switch settings are 1 is softest through to 4 being sport2, the hardest so your switch positions align with expected results.
I reread back through this and I misread your L to N timing, it’s 15 sec from L to N timed when the N light goes solid, the pump continues to run to recharge the height accumulator. Previously you indicated that the ride was good at step position 8 and below (post 20) and Techstream indicates these values in the mid comfort switch positions when you checked (step 2&3 and step 6) so I’m not sure what’s happening.

 

[Kalino_74]

My passenger TB is cranked much more than the driver side. The truck is level from side to side both measuring at 19.75 from hub to fender. Does one being cranked more than the other make any difference on dampning?

 

[PADDO]

Its normal for the two adjuster bolts to not match in length, the driver's side is naturally heavier and it just settles a bit more over time than the passenger side. Common to AHC and non AHC vehicles. The way it should work is that the TBs operate in their linear spring range, providing sufficient torsional force to help support the front of the vehicle in a level way and to provide the right amount of support to achieve a hydraulic preload pressure of 6.9MPa , measured at the pump output or 5.7MPa measured at the damper assembly, at N height. The two shock actuators should have equal hydraulic pressure (they are in parallel unless SLFG is activated during cornering) acting on the same sized pistons so they provide equal lifting forces which are superimposed over the torsional spring lifting force. Together the two combined forces hold the vehicle up at N height, neither force being sufficient to individually support the vehicle. So, you will not have identical mechanical spring forces but should have effectively identical hydraulic forces. My opinion is that the closer the balance of mechanical to hydraulic forces on both sides then the better, and more uniform, the system should operate. Its feasible you'd notice if the two TB's were at opposite extremes of torsional force, but then it's unlikely you'd be even close to cross level at the front. When you do the 16 step test and are in the softer test positions do the front corners take a similar amount of effort to push down and do they rebound similarly? That should indicate how balanced or unbalanced the combined forces are if your damper accumulators are new and equally charged.

 

[Kalino_74]

Paddo, I’m at a loss.... I’ve decide to increase my front pressure some and drive it this way for a week or so in hopes that the new globes will break in some. Once again I appreciate the time you put into helping me. I’ve learned a lot from reading the countless posts on the forum. I’ll keep you updated on my progress.

 

[Kalino_74]

The truck drives sooo good in the 16 step active mode test. I just don’t understand why the damping goes back to being so stiff when not in test mode. I wish I knew what was being bypassed in this test mode because that’s seems to be the culprit. Will it hurt if I keep it in test mode for a few days?

 

[PADDO]

Can you post screen shots of the AHC data list page whilst driving in test mode, when the ride is good, and a shot of driving in normal mode when the ride is $hitty? Ideally similar speeds etc for as valid comparison as possible. In test mode I’d expect to see Ts ON, Ts OFF in normal. Might reveal something.

 

[Kalino_74]

Non test mode

 

[Kalino_74]

Test mode

 

[PADDO]

You’re showing quite a large spread on your front height sensor reading of 0.7 inch in non test and a large range of +/- 0.4 in test. When stationary your height sensors should ideally read 0 at N, with a tolerance of +/- <0.3 inch. You want a small delta and small spread for these values. Height reading snap shots taken when moving aren’t the same as those taken when parked though. Can you post a screenshot of the AHC data list taken in Park on flat level ground, engine running in N. I’d really like to see what the nominal height values are.
Everything else in the two images looked normal except Main Relay Expectation seems blanked in the normal driving test, I’ve only ever seen that ON, never blanked so I’ll do some research. It’s noteworthy to me that the step values were low, soft, but if the ride quality is different then the variable is internal hydraulic pressure ~neutral pressure ~ which we don’t know.