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Intermittent PSM Fault


New member
5 Jun 2022
My 997.1 C2 2005 (UK version) seems to have an intermittent PSM warning light that comes on the dash. The fault code that I read on PSM module is "C150 - Communication DME control unit (drive)".
Local Porsche Specialists told me that this fault is very vague as it basically could be anything on the PSM loop
It can appear as 'PSM fault' on the dash alone or together with 'ABS fault', but 95% of the time it's just the 'PSM fault'.
Usually happens every other time, so 50% chance pretty much if it'll come on.
The warning light usually comes on when the car has been started and will remain until engine off, I've never seen it clear while still driving.
Next time the engine is started it may be gone and when it's gone, it's usually gone for the entire journey. However, I did see occasions where it appears while driving too, although rare. Twice I believe it was triggered when going over a biggish pothole.
Warning might not appear for multiple journeys in a row, but then start appearing again multiple times in a row, usually at the startup.
It's possible to start the car and see the warning, shut it off, restart, and not see the PSM fault again, although I only done it once or twice for testing purposes.

Things already looked at:
- I've replaced the battery to the uprated one myself as for this problem I read that it could be due to weak battery. This changed nothing
- Indy replaced the clutch switch. That did nothing
- Indy replaced the break light switch. That did nothing
- Indy said that PSM module was coded wrong, so they recoded it. That did nothing
- Indy said that they manually went through every single module to see if there could be any wrong coding or other fault that could've caused a chain reaction into PSM. That did nothing
- One Indy Mechanic had told us that we might need to change the abs pump as it could be faulty chip on there, but the other mechanic dismissed it so this was not looked into further
- I've asked Indy if maybe water ingress could be the cause and they dismissed it as unlikely, not been looked into further

If someone can please advise on where to look next
Thank you :worship:
As above... my money would be on a wheel sensor or reluctor ring, as these are used to measure wheel speeds for both ABS and PSM.
You currently have 2 posts on the go for .. somewhat unusual problems ..

They may well be linked so what i say here could well apply to your other post which i will answer after this one .

Is your car a Cab ??

The fault code is not an uncommon one , it often occurs after a flat battery .. voltage drops low and communications between control units drop out .

FIRST test .. get the fault to happen then do a fault code read out of EVERY control unit on the car .. you are looking for communication codes in any of these .. post here after that .

PSM needs the load signal and throttle position , it also feeds back to the DME if it wants it to reduce the throttle position so communication is important .

If you start the car but dont drive it and you get this fault .. i need to know here as its important .. it will relate to something on the self test .. this is something all control units do .. like Pilots do a takeoff checklist before they actually move to confirm everything is ok then your car does the same .

An engine failure ( a component on your car such as abs sensor not working ) happens after takeoff .. car moving .

Fault code here or message and its failed the self test .. this along with your code would indicate a Can Bus failure or a voltage issue .. basically the 2 units cannot communicate so you get a warning .

Can Bus issue / voltage and that certainly could apply to your other post and issue .

Things i can think of causing this ..

Can Bus wiring fault .. you will have codes in various control units for no communication if it is this .

Power distributor pin .... http://911uk.com/viewtopic.php?t=118716&highlight=power+dist

Power supply to dme/psm .. kinda doubt this though ..

PSM control unit power supply or earth issue .

Ignition switch .. an outside but possible fault .

Water ingress .. hence is it a cab .

A failure on a self test routine .. the car is not moving so cant test abs sensors , reluctor rings are not used as such on this model but wheel bearings have magnets in built which do the same job .

Wiring to each one is self tested though .. you would get a fault code for that which isn't what you have reported .
Thank you so much for another comprehensive reply :worship:

The car us UK coupe with a sunroof

I will try to catch it for the readout and post back the results. One thing probably worth mentioning is that I remember seeing Terminal 15 fault as well on some other module, but last time I think it didn't appear.

PSM fault can appear even before I start the engine, just on ignition, but usually only after engine start. Most common situation is where it will be none during ignition and appear as soon as I start the car, without driving. Very rarely I saw it not appear after starting and appearing after driving several yards. Most times if it didn't appear on startup it will be off for the entire journey.
Term 15 is ignition switch in the on position .. in this case a possible fault with the ignition switch .. a test of all control unit fault codes is needed but ignition lock is a possibility .. a donner is what i would do .. we have spares in a draw lets say !

You are into the self test routine though ,, as such the car sees a wiring or communication issue with another control unit .
Ok so I've spent some time with the car and unfortunately I wasn't able to catch the PSM fault during the time I had, sod's law

I did however try and dig out all the codes that accumulated since my last time clearing. I started the car and kept it running while browsing

This time on PSM module there are 2 issues:
C150 Communication DME control unit (drive)
5281 Version coding incorrect

Interestingly, the second code is what my indy already reported before and claimed they coded it right

PAS module
8002 (Upper limit value exceeded) Terminal 15

Instrument Cluster believe this one is due to aftermarket media unit
C141 (No signal/communication) Communication PCM (display)

Front module was surprised to see so many faults
8014 (No signal/communication) Terminal 15 faulty
8010 (No signal/communication) HBA stepper motor, right
8011 (No signal/communication) HBA stepper motor, left
8030 (Lower limit value exceeded) Angle sensor voltage, compression
8032 (Lower limit value exceeded) Compression angle sensor, front
8033 (Lower limit value exceeded) Compression angle sensor, rear
8012 (Lower limit value exceeded) Radiator fan control unit

C152 Communication PSM control unit (drive)
C153 Communication steering wheel electronics control unit (drive)
C150 Communication DME control unit (drive)

C141 Communication PCM (display)

Then while still running the engine, I cleared them all and these re-appered straight away

Front module
8030 (Lower limit value exceeded) Angle sensor voltage, compression
8032 (Lower limit value exceeded) Compression angle sensor, front
8033 (Lower limit value exceeded) Compression angle sensor, rear

C141 Communication PCM (display)

Instrument Cluster
C141 (No signal/communication) Communication PCM (display)

When I catch the PSM light I'll do it again, above look a lil scary though
Sorry , i was short on time last night ..

Ok your faults ..

PCM is a non standard head unit fitted .. won't make any difference to anything .

HBA stepper motor each side .. that's the bit in the headlights that adjusts the beam height .. won't cause hazard light issue or PSM fault .

Angle sensor .. again this is HBA ( Headlight Beam Adjustment ) and its the sensors n/s/f and n/s/r not working , corroded wiring , rod disconnected etc etc .. it won't cause your main faults .

PAS .. term 15 missing .. ok so the alarm unit doesn't know the ignition is switched on .. that WILL cause an issue .. almost like the alarm is triggering but not the siren activation .. no chance of water damage under the n/s/f seat is there ?

Front module .. term 15 missing .. again hazards .. to have 2 modules not knowing the ignition on is starting to look like the issue .. i'm going to guess the PSM or possibly the DME might record this fault if you can get it to happen .

PASM .. again communication issues .

Coding .. sometimes even when coded correctly you get this message .. i would start with looking at gateway coding but basically a coded check of everything which is easier than it sounds as you need to know the exact spec of the car .

I can only guess really as this really is a car i would need to look into but off hand ..

Ignition switch is possible .. not as many codes as i would have liked but at work we have old donner units and i would swop this out first .

The next would be a wiring connection thats corroded , something that links the front , the pas and the PSM together .. a fair bit of studying wiring diagrams there i'm afraid to have a hope .

Then we have to move onto Can Bus wiring .. again it could all be at one connection block .

To me .. i think this is a bit of a difficult issue .. from sitting here anyways and a garage needs to get a bit involved in this .. it maybe a simple ignition lock but it could also be a complicated trace wiring for several hours type fault .
Thank you so much deMort :worship:

Carpets seem dry

I did observe PSM happen and unfortunately didn't see anything new, all the same codes really, so no new clues.
Also I imagine that if there'd be any new codes that they probably wouldn't go away from memory and I'd still be able to read those after?

The G sensor is coming tomorrow so will get that replaced. Since it wasn't mentioned in this thread I imagine it'd be very unlikely.

Ignition switch sounds interesting, I'd be happy to swap it out if I can find a unit, but probably need to know a little more. When buying one does it come with new key blades? Wonder how that works

In general I'd be happy to visit your garage, but it seems you're in Brighton and I'm in Newcastle upon Tyne, quite a trek. However for reference probably would help me to know in case I'd align some UK holidays with a trip :grin:
Would you mind sharing please the name of your garage? Also, if u got spare working units, could u sell one?

I didn't want to overload thread with info when I wrote it up initially, but I've already been at my local porsche specialist 4 times now when they looked at this. In total they probably spent 8 hours with the car. They didn't however suggest anything ignition wise which makes me hopeful as this would be something new to try, although weird as surely they'd seen Term15 fault. I messaged them now anyhow to see what they think, probably more to see if they even looked into ignition (doubt it, as I imagine they'd mention it).

If you'd recommend going to garage again I'd probably try to find someone else as I'm not sure they're telling me the truth. Last time when I've been they said they replaced my non-standard LED fogs with donor ones temporarily, and the problem went away at that time. Even had bumper off. I quickly bought a pair of originals with halogen and incandescent just to be sure and the problem didn't go away. I can't see how it could've been fixed for them but not for me when I replaced them. Maybe I'm missing something? When I told them about it they said they thought that'd be it, but weren't too adamant which I'd expect if they were sure it fixed it for them
Replaced G sensor, flashing hazards and PSM didn't go away

Replaced ignition switch today also, flashing hazards unfortunately still happening, haven't seen PSM yet, but haven't driven it enough yet. Also unsure if anything needs to be recalibrated, reset before drawing conclusions, but my assumption is that if it'd fix anything the effect would be immediate
jev said:
Replaced G sensor, flashing hazards and PSM didn't go away

Replaced ignition switch today also, flashing hazards unfortunately still happening, haven't seen PSM yet, but haven't driven it enough yet. Also unsure if anything needs to be recalibrated, reset before drawing conclusions, but my assumption is that if it'd fix anything the effect would be immediate

Seen PSM too now so none of the issues were fixed so far
I'm so sorry Jev .. i've been inactive for many weeks due to other commitments and health issues and only just seen your post ..

I feel my garage is too far away for that sort of journey but i'm kinda into i would need to look at the car to offer any advice .

You have something strange going on which i can relate to certain control unit issues but as above .. there is only so much i can do on here .

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