DME Voltage Drop

[Lacostas]

Hey All,

So ive been trying to identify why my DME "Supply Voltage" reads around 13ish Volts but the voltage on battery is around 14.3, on my 2004 986 2.7 M96.23

some symptoms:
- Random ABS/PSM Light on
- Huge struggle whenever radiators, AC are on
- Random idle struggles
- Remote key not working (new remote - dealer programmed it but no luck)

Ive already replaced both DME relays but no luck. Next step i guess is the DME Ground point but other than this im out of ideas.

Thanks as always

[mikefocke]

So under electrical load or when at low RPM there is a problem. Have you looked at the charging output? Battery load test?

[Lacostas]

Originally Posted by mikefocke

So under electrical load or when at low RPM there is a problem. Have you looked at the charging output? Battery load test?

Yes but the voltage is always lower in the DME. Plus when i activate AC for example, the DME Voltage almost stays intact but it shoudlnt (afaik).

1. Alternator and VR are new.
2. Battery is 2 y.o and "seems" pretty good
3. Engine ground strap is new
4. Throttle body is new
5. No CEL

I believe that something (corrosion?) is dropping the voltage and DME doesnt see any spikes/drops and thats why it cant "correct" the RPMs on time.

[Lacostas]

I checked the voltage on both the DME relays (Pin #30) and both were showing around 0.3V lower voltage than the battery.

Also measured the C1 fuse voltage and it was the same as the battery. So i guess it may be an issue from the FUSE Box back to the relay ?

[tcoradeschi]

Originally Posted by Lacostas

Hey All,

So ive been trying to identify why my DME "Supply Voltage" reads around 13ish Volts but the voltage on battery is around 14.3, on my 2004 986 2.7 M96.23

some symptoms:
- Random ABS/PSM Light on
- Huge struggle whenever radiators, AC are on
- Random idle struggles
- Remote key not working (new remote - dealer programmed it but no luck)

Ive already replaced both DME relays but no luck. Next step i guess is the DME Ground point but other than this im out of ideas.

Thanks as always

Are you measuring the actual voltage or reading it with Durametric or some other device?

[Lacostas]

Originally Posted by tcoradeschi

Are you measuring the actual voltage or reading it with Durametric or some other device?

Yeap im using my multimeter for this. Initially i found the problem using my iCarSoft reader and now testing with multimeter and the results are pretty much the same.

For now its "Acceptable" but if the voltage drops more then all sorts of issues may arise (i.e injectors?). Obviously changing the entire harness is a no go

Not sure if this can be continued as a DYI tbh so maybe its time for a good electrician

[tcoradeschi]

There are a couple of basics to check - perhaps you have already done these. First thing would be to check the grounding of the DME. See if there is any voltage between it and the negative terminal on the battery? Other than that, trace the 12V line back to the fuse, checking voltage at every connection you can find.

One quick-n-dirty check would be to run dedicated 12V from the battery to the DME to see what you see.

[Danimal]

I am having issues with my locks randomly not working. I checked the immobilizer and there is no corrosion. And changed the passenger door lock actuator, no change.

The locks will usually work in the morning or the first 30ish minutes of driving. Then when the car gets warm or after it’s over or under charged they no longer work. My charging system also reads 14 something at the battery and 13 something per the dme. So I’m wondering if I also have a voltage issue somewhere. Possibly to my immobilizer. My car also chugs a bit with the ac on at idle.

Please keep us posted on what you find.

[Lacostas]

Originally Posted by tcoradeschi

There are a couple of basics to check - perhaps you have already done these. First thing would be to check the grounding of the DME. See if there is any voltage between it and the negative terminal on the battery? Other than that, trace the 12V line back to the fuse, checking voltage at every connection you can find.

One quick-n-dirty check would be to run dedicated 12V from the battery to the DME to see what you see.

Thanks for the input - already tested the ground (i used jumper from ECU ground to battery ground and the voltage was still much lower than the battery).

Im thinking to somehow do the quick-dirty check but im afraid to do it without a fuse in between ..

Maybe i can find somewhere such a fused jumper cable to connect battery all the way back to the DME Relay's (both of them) and recheck DME voltage. Oh by the way both DME relays (PIN 30) showing the same DROP in voltage so i assume it may be something between the fuse box and back.

[Lacostas]

Originally Posted by Danimal

I am having issues with my locks randomly not working. I checked the immobilizer and there is no corrosion. And changed the passenger door lock actuator, no change.

The locks will usually work in the morning or the first 30ish minutes of driving. Then when the car gets warm or after it’s over or under charged they no longer work. My charging system also reads 14 something at the battery and 13 something per the dme. So I’m wondering if I also have a voltage issue somewhere. Possibly to my immobilizer. My car also chugs a bit with the ac on at idle.

Please keep us posted on what you find.

As a first step its good to replace both DME relays (in trunk) and see if it helps. Cost me like 7 EUR each. Then maybe try to measure the voltage on those relays and check where the drop happens and if voltage reaches them intact or lower.