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YOUR RESEARCHDME Voltage Drop - 986 Forum - The Community for Porsche Boxster & Cayman Owners
Reported or suspected cause
same as the battery
Reported cause
No successful repair reported for this finding.
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Reported cause · Original poster
Also measured the C1 fuse voltage and it was the same as the battery.
DME Voltage Drop - 986 Forum - The Community for Porsche Boxster & Cayman Owners
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Leading evidence: 'same as the battery' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'same as the battery' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check but im afraid' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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1
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Performed · outcome unconfirmed
I checked the immobilizer and there is no corrosion.
DME Voltage Drop - 986 Forum - The Community for Porsche Boxster & Cayman Owners
Check voltage
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Performed · outcome unconfirmed · Original poster
I checked the voltage on both the DME relays (Pin #30) and both were showing around 0.3V lower voltage than the battery.
DME Voltage Drop - 986 Forum - The Community for Porsche Boxster & Cayman Owners
Replace dme relays
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DME Voltage Drop - 986 Forum - The Community for Porsche Boxster & Cayman Owners
Test ground (i
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Performed · outcome unconfirmed · Original poster
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).
DME Voltage Drop - 986 Forum - The Community for Porsche Boxster & Cayman Owners
Coverage and how to read this overview
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
10 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
986Forum: 1 discussions
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Generation: 20261027T003124Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
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
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.
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 ?
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
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.
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.
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.
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.
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