P38A EAS Random Extended Mode Selection

So yesterday I went to Bedford to sort my AC compressor & get the system re-gassed. That all went well.

On the way back down the M1, the EAS went into "random extended mode" again a few times (i.e. the non-selectable height above high-mode). Mostly this happend at low speed in traffic (<<25mph). As usual no faults in the ECU escept the usual "invalid / unknown fault code" !! This time I was recording the EAS on Nanocom, so got some data.

What I did notice when it happens is the rear has gone a bit high compared to the targets, and was not dropping even though the Exhaust & corner valves were being commanded to open. My suspicion is the connection between driver pack & the solenoids, so if I get time this weekend I will be taking the valve block out for a check.

Lines 644, 811 & 1010 show it happening. As usual hitting the Down button seems to drop the car, and prevent fault mode.

Wondering what others think ?

I'd go check the sensor in question before pulling the block. I was watching my sensor behavior on the live data nano and seeing the rear left glitch as it went from access to wade and back again. It would climb and drop while going through it's value cycle

Mark, I'm gonna do that as well. Strangely 3 of 4 sensors behave quite differently to the Rear Left, which gives much smoother output. They have all been like this since I bought the car. Never replaced any.

The two bunps on the rear sensors are when it went to extended mode, but to me appear to be the result rather than the cause.

If I was seeing much wilder varations before the jump, then yes I would suspect a sensor.

pwood999 said:

Mark, I'm gonna do that as well. Strangely 3 of 4 sensors behave quite differently to the Rear Left, which gives much smoother output. They have all been like this since I bought the car. Never replaced any.

The two bunps on the rear sensors are when it went to extended mode, but to me appear to be the result rather than the cause.

If I was seeing much wilder varations before the jump, then yes I would suspect a sensor.

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Agreed, if it was one sensor I'd go for thatbut... Hmmmm

A duff electrolytic in the driver pack can give strange results such as you describe.

Pull the kick panel from passenger side Foot well the big white connector usually has corrosion. Switch cleaner only or cut it out and hard wire it

Connector soldered many years ago !!

Driver pack bench test is next step.

pwood999 said:

Connector soldered many years ago !!

Driver pack bench test is next step.

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Might not show anything on the bench unless you have a full system, it's back EMF from the solenoids not being absorbed my the electrolytic that kicks the firmware out of kilter.

Agreed, but initially I'm looking for intermittent connections on the wires entering the pack, and the solenoid connector.

I did think about extending the test rig to include the ECU, but abandoned that idea years ago !!

pwood999 said:

Agreed, but initially I'm looking for intermittent connections on the wires entering the pack, and the solenoid connector.

I did think about extending the test rig to include the ECU, but abandoned that idea years ago !!

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I started a test rig complete with spring return air cylinders to represent the 4 corners as I have a complete set of spares from my scrapper. I gave up as the EAS has proved pretty reliable so the rig has not been needed.

Mine also(forgot to mention and now I remember ) would go into extanded height on occasion, since I had the defective sensor. Do a test with your ohms meter in the two rears for glitching

Took the valve block out for bench test today. Connected up my manual control box & tried each solenoid multiple times whilst wiggling the connections on the driver pack, and also the black solenoid wires. Definitelty 2-3 dodgy connections to the solenoids, but not the wires entering the driver pack. This could explain the strange behaviour if the ECU doesn't get the expect height changes, especially if the solenoid operation was intermittent.

Tested each socket contact using a spare pin from a pressure sensor. At least 6 out of 12 were quite loose, so de-pinned the contacts (one at a time), and squeezed them gently so the pin made firm contact. No corrosion visible but sprayed them with contact cleaner anyway for good measure. The connector was rather tight when plugging back in !! Re-testing with manual control, and could no longer find any intermittent connections - all solenoids operating every time now.

Re-assembled into a spare housing because the original has two loose compressor mounting studs. All back in the car. Pumped the tank up to 100psi via the dryer pipe using garage compressor, and then raised the car manually for leak checks. Finally reconnected compressor, and let that finished filling the tank.

Only done local drive so far, but a longer drive will show if that fixes the problem. Didn't get time to check the height sensors, but there were no strange readings on the recording, so I'm hopeful on those !!