Advice needed

[Harnekrai]

Hi ,I have avidly read the forums on piston heads and have decided to join. I have a 996 Carreras 2 cabriolet. It has recently shown the check engine light. This is on constantly and associated with this warning light the fuel gauge light and the thermostat lights are on constantly. The rev counter also not working. The car starts normally and runs normally. I have had it plugged in at two local mechanics and the error codes are 35 at one mechanic and 26 at the other!!!! One mechanic tells me it is related to the immobiliser and the ECU, the other mechanic has diagnosed a problem with the alternator which he is going to replace and hopes the warning lights settle down. He also mentioned a problem with the 'W' wire ???
I am reluctant to send it to a OPC as it will no doubt cost me an arm and a leg. Has anyone come across this problem before.?
Thanks in anticipation

[Rockster]

Harnekrai said:

Hi ,I have avidly read the forums on piston heads and have decided to join. I have a 996 Carreras 2 cabriolet. It has recently shown the check engine light. This is on constantly and associated with this warning light the fuel gauge light and the thermostat lights are on constantly. The rev counter also not working. The car starts normally and runs normally. I have had it plugged in at two local mechanics and the error codes are 35 at one mechanic and 26 at the other!!!! One mechanic tells me it is related to the immobiliser and the ECU, the other mechanic has diagnosed a problem with the alternator which he is going to replace and hopes the warning lights settle down. He also mentioned a problem with the 'W' wire ???
I am reluctant to send it to a OPC as it will no doubt cost me an arm and a leg. Has anyone come across this problem before.?
Thanks in anticipation

Those numbers are probably Porsche internal error codes. Are there any other codes you can share? Error codes like P0600, P0601, P0616, or U0001, U0167 or U0168? Not these exact codes, perhaps, but error codes that start with a P or a U or some other letter (B or C IIRC) and with 4 digits.

The security module if it is sick is quite capable of providing error codes when queried and these can be used to know what part of the system is acting up. If a tech tells you the security module is bad then perhaps he is working from error codes? If so he should share that with you, that is share how he arrived at his diagnosis.

It is rare the security module itself goes bad. Those that do go bad often do so when they get wet. They get wet from water getting into the cabin. The most common path is from overflowing body water drains which get plugged up and allow water to collect in their catch basins and overflow into the cabin. The security module is located in a particularly bad spot (low and under a seat).

Another possible explanation is mice have been at the car and chewed some wiring. If you tell me the car has been parked up with little to no use for weeks at a time... Mice or rodent sign is not hard to spot but it has to be really looked for.

The alternator is not as smart as the security module so it can't be queried but the error codes could point to a power level problem. BTW, a low power level can trigger error codes from other controllers and the security module is one.

My WAG based on the symptoms is the alternator, though I would ensure the battery is in tip top shape and the cabling between the battery and the car -- all battery leads! -- are in also tip top shape. A sick but still functioning battery, or marginal cabling or cable connections, can wreck havoc on a modern car, generating seemingly unrelated symptoms, behavior, and error codes.

If it is the alternator, what can happen is the alternator for some reason can't supply enough power to meet the car's electrical needs. The engine may continue to run with no symptoms but other electrical components do not like insufficient electrical power. The instrument cluster controller, security system controller, and some safety restraint (air bags) or safety control systems (like ABS or PSM) may react to too low electrical power and generate warnings/error codes.

I would not replace the alternator on my WAG. One wants to be sure. While either the security module or alternator can be at the root cause one wants to know for sure in order to replace the bad part. Both the security module and alternator are expensive and the tech has to be sure, should be sure. That you have two that disagree and do so based on a difference in error codes suggests to me that maybe you need a 3rd opinion and let the majority rule.

But try to pry out any error codes, Porsche specific or more generic, from both. Also, you can I guess approach both with the conflicting diagnosis and ask they reconcile their diagnosis with the other tech's.

[LukeS]

Not sue if this helps

http://forums.rennlist.com/rennforums/993-forum/15...

[Orangecurry]

First rule with any electrical problems is to ensure your battery and grounding point(s) are good.

I would get a new (quality) earth strap, clear any corrosion on the connecting point to the chassis, and ensure the battery is a good/new one.

Then, even if that makes no difference, you can start to find the actual problem.

[Harnekrai]

Hi thanks for all the useful advice and website. The update is that the alternator was not charging as it should have been and so needed changing anyway. Once a refurbished Bosch alt was fitted the faults all seemed to sort themselves out!! The warning lights have gone out and the rev counter back working.
Cost me £400 all in- ouch , but I'm sure still cheaper than OPC. You were right low power can lead to all sort of strange errors/ warning lights.
Thanks once again
Harnek