P38A Phantom gearbox/alternator/EAS fault

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alexmcrobbie

alexmcrobbie

Member
Posts
80
Location
Glasgow, Scotland
Hey Folks,

So I’ve had a recurring fault on my 2001 P38 Westminster with the 2.5 Diesel engine (autobox). The fault had been occurring about once every 2 months until recently when it has started happening almost daily.

Essentially what happens is that any time up to 20mins from startup (usually sooner) a series of faults occur at the same time.

The chain of events usually follows this sequence:

• “GEARBOX FAULT” displayed in message centre.
• “ALTERNATOR FAULT” displayed in message centre.
• EAS light on gauge cluster illuminated and all 4 EAS position lights stay on solid.
• Engine RPM gauge drops to 0.
• Engine revs erratically for a period up to 20 seconds with limited response to throttle.
• Rev counter comes back to life and EAS returns to normal.
• Gearbox becomes locked in 3rd gear at all speeds until engine has been turned off and back on again.


From the research I’ve done so far I know of a few possible causes for this peculiar behaviour including a weak battery, failing alternator or corroded ground straps. Replacing the battery with a beefy new Yuasa Black Series (tested multiple times and known to be good) hasn’t solved the issue. Nor does the fault appear to be as a result of a bad alternator (this was replaced for a new & genuine part which also didn’t solve the issue (voltage at alternator @2kRPM 14.4V with no drop to battery)). I’ve checked most of the ground straps with the ol’ multimeter and they all seem good (some new straps on the way nonetheless).

I was just wondering if anyone has had the same issue and found it to be caused by anything other than battery/alternator/ground wires, or if anyone might be able to shed some light on the issue.

I’ve attached a pic
350ADB4F-0160-4FBF-8FED-ED42988F109C.png
22BF83B4-E70C-4A70-B42F-E6EB6A3BB78B.jpeg
(hopefully) which shows the fault during driving ( albeit after some of the the messages had cleared).


Thanks in advance!

Sandy.
 
I have had the same issue (twice).
Each time it was a replacement Alternator.
Started off as the occasional message centre bleep with:
AES Fault or Gearbox Fault or ABS Fault or Traction Control Fault.
Then progressed to "bouncing" rev-counter "Actual Revs" - Zero Revs - "Actual Revs".
Not surprisingly, mine escalated after I ran up a kerb and there was a sharp jolt through the car which then produced an apparently totally dead binnacle unit.
I took the car home immediately and stuck a DVM on it and found barely 12V across the battery even with the engine running.
First time I paid the indie the full whack for anew alternator + fitting.
15 months later I had it all over again. They tried to charge me for the replacement plus fitting but I asked to speak to the boss and asked him if he thought an alternator was a consumable or a "lifetime" part.
He agreed and the bill was cancelled and the parts + labour were charged to his part supplier as the unit was clearly faulty.

So, my experience has been that the Alternator's all too easily blow, especially aftermarket ones.
 
Sorry, just a quick thought.....
On mine (P38A Motronic) the Alternator showed a healthy 14.x volts most of the time. EXCEPT when I had the binnacle/instrument cluster rev counter issue showing zero RPM.
That's when the DVM showed there was barely 12V at the battery terminals.
All the sub-system (AES/Traction etc.) alarms were merely transitory. Usually appeared straight after starting when the battery had taken the initial start-up hit (so Amps drawn out = reduction in available volts I think).
A new battery was my first change and I thought it had "fixed" the issues ......until the failing alternator caused the new battery to have the stuffing knocked out of it too.
As the alternator was "iffy" and barely keeping pace with daylight driving loads the systems all recovered enough to run (just).
When the Rev counter started swinging between true revs and "0" something had caused the alternator to deliver little or no volts and the battery alone although new was unable to satisfy demands.
Hope this helps.
 
DanClarke said:
Sorry, just a quick thought.....
On mine (P38A Motronic) the Alternator showed a healthy 14.x volts most of the time. EXCEPT when I had the binnacle/instrument cluster rev counter issue showing zero RPM.
That's when the DVM showed there was barely 12V at the battery terminals.
All the sub-system (AES/Traction etc.) alarms were merely transitory. Usually appeared straight after starting when the battery had taken the initial start-up hit (so Amps drawn out = reduction in available volts I think).
A new battery was my first change and I thought it had "fixed" the issues ......until the failing alternator caused the new battery to have the stuffing knocked out of it too.
As the alternator was "iffy" and barely keeping pace with daylight driving loads the systems all recovered enough to run (just).
When the Rev counter started swinging between true revs and "0" something had caused the alternator to deliver little or no volts and the battery alone although new was unable to satisfy demands.
Hope this helps.
Click to expand...

Hi Dan,

Can’t thank you enough for your insight. That would explain why the voltage output from the alternator usually looks good (as I’ve not been able to check it whilst the faults have been occurring). Might throw another alternator on as they’re not too expensive for a Bosch job.

Sandy.
 
alexmcrobbie said:
Hi Dan,

Can’t thank you enough for your insight. That would explain why the voltage output from the alternator usually looks good (as I’ve not been able to check it whilst the faults have been occurring). Might throw another alternator on as they’re not too expensive for a Bosch job.

Sandy.
Click to expand...
You are very welcome Sandy.
There are a few places still that will repair Alternators (new slip-ring and/or Diode-packs) and I have my failed original Bosch Alternator (150A) from the first change, so I really should get it repaired...because you never know.
Hope you get to the bottom of your problem. The last change on my old Rangie was good and still is (as far as I know).
 
DanClarke said:
You are very welcome Sandy.
There are a few places still that will repair Alternators (new slip-ring and/or Diode-packs) and I have my failed original Bosch Alternator (150A) from the first change, so I really should get it repaired...because you never know.
Hope you get to the bottom of your problem. The last change on my old Rangie was good and still is (as far as I know).
Click to expand...

Yeah it would be great to finally get the issue resolved. I’ve been pretty lucky get evey time it’s happened I’ve been in a safe position. However, I can just imagine the problem occurring whilst merging onto the motorway and really don’t want that to happen and create a dangerous situation.

Sandy
 
It's almost definitely a low voltage issue somewhere. Mine used to throw up all the same faults before I replaced the battery.
If the alternator doesn't fix it, start looking at the multi plugs to the BECM and also check your fuse box under the bonnet. It's a known weak spot.
 
Thanks guys, I would definitely agree that the symptoms are indicative of a low voltage somewhere in the system and, as we all know, the P38 is all too easily upset by that.

Strangely, there's a healthy 14.2-14.3V at the battery at idle and 14.4V at the battery at 2k RPM which would suggest that the alternator and wiring (to the battery at least) are ok.

One thing I did forget to mention is that when the car is at idle and I flash the high beams, turn the steering or put the car in gear there is a slight (but noticeable) blip from the engine where the revs drop by at least one mark on the instrument binnacle before returning to normal. The car has done this for the duration of my ownership (18months) and I wonder if there's any relation between this and the more serious faults the car has been presenting.

UPDATE: Have also been getting EAS FAULT displayed on the message centre once every few days recently (accompanied by all the EAS position lights turning on) despite all air bags being less than 3 months old. The compressor rarely runs in daily use and was overhauled in the last year, so I suspect this message may also be part of the wider electrical fault.

Sandy.
 

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Hi Guys,

So to update on what’s been happening.

I hooked the car up to the lynx tool today and whilst looking at the live data for the gearbox was surprise to see the engine speed at 64rpm despite the engine not running.

Anyway, I took the car for a run with the lynx connected and all seemed fine (with the live engine speed reflecting the engine speed displayed on the instrument cluster). However, when the phantom fault eventually occurred, I noticed that the live data showed 64rpm again despite the engine now running at probably around 1500rpm (while the strange fault(s) was/were happening)

I’m wondering if perhaps the Crank Position Sensor is at fault? Does anyone know where the gearbox receives it’s engine speed data from? If it’s the Crank position sensor then surely this will be a good place to start.

For reference, the gearbox live data continues to display a battery feed voltage of 13.1V or thereabouts while the fault occurs, so I’m thinking I could potentially rule out the fuse box/alternator/battery/ground wires at this point?

Attached is a photo of the fault codes stored for the gearbox. These return as soon as they have been cleared.


Cheers again,
Sandy
 

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Also, I’ve just been out again with the Lynx connected (monitoring engine live speed again)

Whilst coming to a stop the engine died and you can see on the live graph read out attached that the engine speed signal fell again to 64rpm when this happened.

Starting to feel quite puzzled by this one.
 

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The plot thickens.

Perhaps also worth mentioning that the following faults have now appeared on the EMS which were not present before

136 Fuel Flow Actuator Circuits
11 Lost Communications With Fuel Injection Module
133 Charge Pressure Sensor (B5/1)
 

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No expert and never played with a Lynx but I think the engine speed would drop to zero if it stalled, wouldn't it? I guess it might lose communication around that point too. Have you tried checking the relays in the fusebox are fine by giving them a bit of a push/wriggle while running?

Charge pressure sensor? Is that the MAP? There's a pipe from the fuel filter to the inlet manifold, you could check that is in place and not split.

The crank sensor has to be a set distance from the teeth so might be worth checking that. @wammers knows the spec.
 
Grrrrrr said:
No expert and never played with a Lynx but I think the engine speed would drop to zero if it stalled, wouldn't it? I guess it might lose communication around that point too. Have you tried checking the relays in the fusebox are fine by giving them a bit of a push/wriggle while running?

Charge pressure sensor? Is that the MAP? There's a pipe from the fuel filter to the inlet manifold, you could check that is in place and not split.

The crank sensor has to be a set distance from the teeth so might be worth checking that. @wammers knows the spec.
Click to expand...

I've not really played with Lynx much (should probably have bought a nanocom tbh) but it seems to be giving some clues.

Assuming charge pressure refers to the MAP yeah. I'll have a look at the pipe you're talking about for sure, but I suspect this is a fault of the electrical variety.

When the engine stalled I would also have expected to see 0rpm rather than 64rpm. As mentioned, when the fault occurred (and engine revs were really around 2000rpm), the gearbox was observing 64rpm again. This leads me to think that perhaps it's the crank position sensor that's faulty (as this would also result in a dead tacho).

However, I would suppose that a faulty alternator could also cause the same selection box of faults...

I'll take a look at the crank sensor tomorrow and see if I can spot anything dodgy. Would assume the oil leak down that side of the engine wouldn't interfere too much with the Crank Sensor plug if it's supposed to be waterproofed...

At a stage where I'm considering flipping a coin over which to buy first, an alternator or Ck Position Sensor. haha! ;)
 
I'm wondering if you've got a dodgy ecu here. 64 as a decimal number is just too convenient when talking computers etc.
Computers only know on and off and 64 just happens to be one of an array of bits being "on" (1,2,4,8, 16,32,64 etc etc etc)
I'm just wondering if something withing the ecu is failing and occasionally it makes this bit stay on and throws it all over the place?
Not sure how you could find it apart from substitute ecu.
 
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