All sorts of warning lights!

911Heaven · 18 Nov 2016

Hi guys,

I had an engine rebuild on my 2002 996 3.6 C2 not too long ago (just over 2 years ago), and cause or not, when I got it back it had a new battery installed as well (rubbish one, now replaced), and some fuses had blown, causing the radio not to work. I figured it may have been jump started or fast charged with resultant spikes causing the fuses to blow.

So when it came back, I had an assortment of errors that are still ongoing, yet intermittent. I replaced the audio fuses when I got it back and all was ok. Recently the screen of the PCM gave way, not sure if related or not, over 2 years later - probably not, but just including as a matter of course.

The errors that have been difficult to track have been listed below.

When driving, and when came back from rebuild over 2 years ago until current:

- Intermittent oil pressure sensor failure warning, gauge looks fine otherwise when working
- Intermittent water temp sensor failure warning - needle takes a long time to climb to operating temp also. I was thinking that the stat may have been stuck open, but don't think so. I presume it's the sensor or an electrical fault, due to the other faults present.

Can't remember if both sensors were replaced, but I think the water temp sensor was.

Recently (last couple of months):

- Despite recent new battery and alternator check, alternator light comes on periodically.

I just wonder, having replaced (some or one) of the sensors, what else could it be? Are these issues related? On the same circuit?

Maybe it's not the sensors themselves because replacing one didn't work, and it's intermittent.

Something to do with getting it back from this garage? Spikes?

Refurbishing the car and want to get all the little niggles sorted, having owned the car for over 8 years.

I personally think something has been damaged, as the electrical faults seem more blanket, than specific, especially given the surrounding picture.

What are your thoughts guys?

Luke.

Halcyon · 18 Nov 2016

bit of a guess, but could it be the actual instrument binnacle / cluster?

I've heard that the oil pressure gauge can fail in the cluster.. I'm sure DeMort will be along shortly!!

deMort · 18 Nov 2016

Blimy .. no pressure then lol

Im thinking atm i could probably write pages on this on what it could be etc ..

need to break it down a bit though .

Faults when it came back are blown radio fuse , temp sensor issue and oil pressure issue ..

After 2 years then any other issues are imho going to be new ones ..

Pcm .. its died or has a blown fuse .. check feeds/earth at the back of the unit if ok and no fuse blown then its dead .. nothing to do with the engine .

Alternator light .. either an old alternator with worn comutator or brushes or possibly a corroded lead running to the battery .. it goes via the starter and has a connection on the gear box both of which can corrode and cause a resistance .. my bet would be you need a new alternator .

Leads can be checked .. voltage drop from alternator to battery would check this ( more info if req )

Faults from engine work ..

Radio fuse .. its a hell of a spike to blow it .. possible though as is jump starting with the leads the wrong way around .. i would expect more damage though but not to engine sensors .

Coolant temp .. is it a tip ? theres a valve that sticks causeing slow warm up .

I would start with temp sender repacement and looking on a tester , might be fault codes or actual values of live data that may help .

Oil sender .. i would replace it first .. if you had low oil pressure then im sure you would know about it by now .

Instrument cluster fault .. you get them but these are very different systems .. it may have a shared earth .. there are small earth leads on an engine but it would take a lot of studying wireing diagrams to see if theres a link ..

But i would certainly start with those sensors being replaced then investigate further .. its not a huge expense .

Let me know if its a tip ..

Let me know if the temp sender has actually been replaced

If you can check the pcm feeds/earth

If you can check the voltage output at the alternator or the jump post and then at the battery .. i need to know the voltage difference at idle .

You can PM me if you want but most people love to read things like this and it would spoil it for them .. so im told lol .. so here is perhaps better to stop me getting moaned at

Thats all i got atm as im tired .. i was up at 6 this morning and im old

.. well maybe not !

Ive also got a load more posts to look at .

911Heaven · 19 Nov 2016

Hi Demort,

Thanks for the long reply!

To answer some of your questions:

- Voltages at Idle:
Jump post: 14.25V
Battery: 14.05V

- Water temp sensor, replaced trying to find intermittent fault, just after rebuild, April 2014. The fault remained however, and it does take a while to get to temp. When it does, the reading seems fine. Every now and then it throws a light and the gauge drops off.

- It's a Tip.

- Oil pressure sender: Not replaced, this may have been a later issue, so probably a replace job.

- Instrument cluster, not sure. Everything else seems ok.

- Alternator was replaced about 3 years ago, but tested Ok recently. Light driving since replacement.

- PCM - this is being repaired now, but aside from the blown fuses to audio, the screen went only recently so probably not related. The unit doesn't power on, presumably to protect itself from excessive current draw from faulty screen inverter / driver etc. It did hiss for a bit sometimes after. Interestingly, I did hear the sound system, with no screen, fire up not long ago for a few seconds! But anyway, that's a detour!

Only other thing to mention, key barrel has been recently replaced, but for a while the switching was very temperamental!

Thanks, Luke.

Demort said:
Blimy .. no pressure then lol

Im thinking atm i could probably write pages on this on what it could be etc ..

need to break it down a bit though .

Faults when it came back are blown radio fuse , temp sensor issue and oil pressure issue ..

After 2 years then any other issues are imho going to be new ones ..

Pcm .. its died or has a blown fuse .. check feeds/earth at the back of the unit if ok and no fuse blown then its dead .. nothing to do with the engine .

Alternator light .. either an old alternator with worn comutator or brushes or possibly a corroded lead running to the battery .. it goes via the starter and has a connection on the gear box both of which can corrode and cause a resistance .. my bet would be you need a new alternator .

Leads can be checked .. voltage drop from alternator to battery would check this ( more info if req )

Faults from engine work ..

Radio fuse .. its a hell of a spike to blow it .. possible though as is jump starting with the leads the wrong way around .. i would expect more damage though but not to engine sensors .

Coolant temp .. is it a tip ? theres a valve that sticks causeing slow warm up .

I would start with temp sender repacement and looking on a tester , might be fault codes or actual values of live data that may help .

Oil sender .. i would replace it first .. if you had low oil pressure then im sure you would know about it by now .

Instrument cluster fault .. you get them but these are very different systems .. it may have a shared earth .. there are small earth leads on an engine but it would take a lot of studying wireing diagrams to see if theres a link ..

But i would certainly start with those sensors being replaced then investigate further .. its not a huge expense .

Let me know if its a tip ..

Let me know if the temp sender has actually been replaced

If you can check the pcm feeds/earth

If you can check the voltage output at the alternator or the jump post and then at the battery .. i need to know the voltage difference at idle .

You can PM me if you want but most people love to read things like this and it would spoil it for them .. so im told lol .. so here is perhaps better to stop me getting moaned at

Thats all i got atm as im tired .. i was up at 6 this morning and im old .. well maybe not !

Ive also got a load more posts to look at .

infrasilver · 19 Nov 2016

The temp sender issue could be a chafed wire as they are tight going down the back of the engine where it meets the sensor wiring, I has issues with mine and ended up cutting the wires and re-soldering, never had an issue since. You need to inspect this and it's reasonably easy to get to once you remove the airbox. Also check the multi plugs and make sure the connections are clean before it goes into the car and on to the ECU.

911Heaven · 19 Nov 2016

Thanks for the shout here, will check! At least it could be localised.

Luke.

infrasilver said:
The temp sender issue could be a chafed wire as they are tight going down the back of the engine where it meets the sensor wiring, I has issues with mine and ended up cutting the wires and re-soldering, never had an issue since. You need to inspect this and it's reasonably easy to get to once you remove the airbox. Also check the multi plugs and make sure the connections are clean before it goes into the car and on to the ECU.

deMort · 20 Nov 2016

It sounds like the temp fault is 2 different issues .. it takes a while to warm up and when at temp it sometimes drops out and flags a message ..

infrasilver has already answered the second ..

The first might be the grey electric valve on the side of the Tiptronic thats failed .. it causes the oil cooler for the tip to be permanently open and the coolant will take longer to get to temp as it basicaly bypasses the thermostate.

Easy enough to check .. look at the valve next to it and when engine is started it should move ( vacum operated valve ).

http://www.deroure.com/diagrams.asp?TBL=2577&MAK=3&MDL=25&SMA=0&SMO=0&ST=&SC=0

No 14 is the vacum valve .

The leads would appear to be ok from the alternator but im not convinced the alternator is ok .. i would leave it for now and monitor .

1 other possible is the blue wire that goes from alternator to instrument cluster is damaged .. but i would have thought if that then the car would either start with the fault or be fine after starting and not come on when driveing .

Oil sensor replace to start with and perhaps check this ..

http://911uk.com/viewtopic.php?t=116389

But i doubt that will be broken .

Key barrel replacement is not unusual these days but once replaced it would fix any problems .

Griffter · 21 Nov 2016

If I were you I would methodically check, clean and tighten all earths and connectors in the engine bay, especially to and from the alternator. A lot gets disturbed when an engine is replaced and may be put back in a hurry.

Osh · 21 Nov 2016

'afternoon Heaven/Demort

I have the same issue with the Oil sender; i've had mine replaced but still have an intermittent failure that i'm trying to get my car booked in for right now (that and the drivers seat keeps fusing).

The feedback suggests a chaffed wire somewhere in the loom for the sender - i might be driving along and the gauge just stops working and the warning light comes on - the within seconds it will start again.

With the drivers seat i can change the fuse and it might work for anywhere between a few mins and few days before blowing (this means Mrs Osh cant drive the Porker... :thumb: )

Osh

deMort · 21 Nov 2016

Well .. the engine is at the back of the car .. gauge at the front and theres several wireing connections along the way that might have a loose connection .. my money would be on the wireing loom connection thats right side of the drivers seat under the carpet and a panel haveing a poor connection .

Its a case of wireing diagrams out and traceing the wire from engine to the gauge.

Basically it sounds like when hitting a bump theres a conection somewhere makeing and breaking the circuit .

The seat .. you have a chaffed wire somewhere under the seat thats shorting out .. i would remove the seat and check.

If it blows when operateing then its possible a partailly seized motor or cable could be the fault .. either way its seat up .. operate and check .

Osh · 22 Nov 2016

Demort said:
Well .. the engine is at the back of the car .. gauge at the front and theres several wireing connections along the way that might have a loose connection .. my money would be on the wireing loom connection thats right side of the drivers seat under the carpet and a panel haveing a poor connection .

Its a case of wireing diagrams out and traceing the wire from engine to the gauge.

Basically it sounds like when hitting a bump theres a conection somewhere makeing and breaking the circuit .

The seat .. you have a chaffed wire somewhere under the seat thats shorting out .. i would remove the seat and check.

If it blows when operateing then its possible a partailly seized motor or cable could be the fault .. either way its seat up .. operate and check .

Ta m8 :thumb:

Osh

911Heaven · 24 Nov 2016

Hi Demort,

Thanks, makes sense about the valve!

Regarding the alternator, when the light does come on (more often I think when car is starting, the voltage drops below 12v, then when fault light disappears, goes above 14 again. It's not every trip either...!

Luke.

Demort said:
It sounds like the temp fault is 2 different issues .. it takes a while to warm up and when at temp it sometimes drops out and flags a message ..

infrasilver has already answered the second ..

The first might be the grey electric valve on the side of the Tiptronic thats failed .. it causes the oil cooler for the tip to be permanently open and the coolant will take longer to get to temp as it basicaly bypasses the thermostate.

Easy enough to check .. look at the valve next to it and when engine is started it should move ( vacum operated valve ).

http://www.deroure.com/diagrams.asp?TBL=2577&MAK=3&MDL=25&SMA=0&SMO=0&ST=&SC=0

No 14 is the vacum valve .

The leads would appear to be ok from the alternator but im not convinced the alternator is ok .. i would leave it for now and monitor .

1 other possible is the blue wire that goes from alternator to instrument cluster is damaged .. but i would have thought if that then the car would either start with the fault or be fine after starting and not come on when driveing .

Oil sensor replace to start with and perhaps check this ..

http://911uk.com/viewtopic.php?t=116389

But i doubt that will be broken .

Key barrel replacement is not unusual these days but once replaced it would fix any problems .

911Heaven · 24 Nov 2016

Thanks everyone for their replies. Seems as though all the right angles have been covered, so lots to check.

I think we secretly love the issues we hate don't we!

deMort · 24 Nov 2016

I love the faults .. its a challenge

If the alternator light mainly comes on when starting ( i assume it goes off not long after or volt gauge goes to 14v ) then its a low voltage supply problem to the alternator i would guess at .. i thought pretty much any voltage would exceite the alternator windings but i might be wrong .

maybe engine earth strap .. possible resistance in the blue exciter wire .. not sure but something else to check .

Tiptronic coolant valve is certainly one to check .. let us know if not and we can carry on " diagnosing "

911Heaven · 6 Dec 2016

Hi Demort,

Whilst I have just had my oil filler neck replaced, I noticed that the voltage is now fluctuating, and below 14v. Starting to think, not a loose connection or bad earth...

And potentially a source of sensor failures, although perhaps not fully or at all.

Do you think it's worth going straight for new alternator? It's about 4 years old I think...

Demort said:
I love the faults .. its a challenge

If the alternator light mainly comes on when starting ( i assume it goes off not long after or volt gauge goes to 14v ) then its a low voltage supply problem to the alternator i would guess at .. i thought pretty much any voltage would exceite the alternator windings but i might be wrong .

maybe engine earth strap .. possible resistance in the blue exciter wire .. not sure but something else to check .

Tiptronic coolant valve is certainly one to check .. let us know if not and we can carry on " diagnosing "

All sorts of warning lights!

911Heaven

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