986 2003 2.7 faulty DME, any experts here?

Hi Guys I have cross posted this here to the 996 forum because of system similarity. Mod's please remove if not happy. I rather cleverly damaged my DME when I cut through the pre cat o2 sensor wires while the car was running. So now that sensor has a P0134. I have tried 2 different known working sensors and been through the whole diagnostic procedure. So damaged DME is all I am left with. Car runs great apart from that, just check engine light, and no o2 related activity on bank 1 now (no fuel trimming etc). I was awaiting a replacement matched DME/Alarm/key set, but have cancelled it because it came from a manual car and mine is a Tiptronic. The part numbers are all identical, but it seems it will have a different "flash" on it. So while I am hunting for a matching Tip set at a reasonable price, can anyone tell me what part of the board I will have damaged on the DME? I have had that apart and can not see ant evidence of burning or damage. There are companies that will rebuild them, but if I can get a less expensive way forwards then that would be good given my current circumstances. Not holding out much hope, but you never know! There is a lot of expertise here. I may cross post this on the 996 forum as its a very similar DME set up. Many thanks Berni

Have you checked all your fuses? I don't have a 986 wiring diagram, but I seem to remember a "pull out" small fuse box in the rear trunk behind the left panel that had a Secondary air pump fuse and some 02 sensor fuses in it, might check there.. ( it's been over a decade since I have worked on a 986)

Hello, Thank you for the suggestion, but sadly not (AFAIK). I have been through the full diagnostic cascade, and have continuity where there should be, within spec resistance, 415mv on the signal wire (bit low). Everything checks out unfortunately. Berni

Quotes source post: 16972462

The 02 sensor has a heater circuit that needs a 12v power source and a ground to heat the 02 sensor. If the heater circuit is not working, the 02 sensor will not work cold or idling. Check for 12v power and ground ( using a wring diagram), if not ok check fuses mentioned.

Hi Thank you, Yes have 12v on the heater wire and a good ground. That would throw a different code as I understand it. I was stupid enough to have cut the wires while live in the first place so could certainly have missed something basic in the diagnosis. But I think not. Many thanks! Berni

Quotes source post: 16972508

You have 4 wires, 2 grounds and 1 power wire 1 sensing, if both grounds are good, and you have 12v for the heater, then check sensing AT THE SENSOR by forceing rich/lean by creating a large vacuum leak and spraying addition fuel/propane in the engine to see if the sensor follows the rich/lean you commanded.. If the sensor follows the commands, it is working, then check them at the DME.. Hope this kind of tests are not too advanced for you..

Quotes source post: 16972548

Hi, yes OK, I can do this, so I tap into the sensor black sensing wire with my meter with everything connected, and track voltage as I spray easy start into the intake, then pull a vacuum pipe. I do have a Durametric which monitors sensor voltage, can I use that to monitor voltage as I perform the test? Just checking I am following your thinking. Thanks for the suggestion, its a good one and I have not tried it. Berni

Quotes source post: 16972564

You can use Durametric to monitor sensor action, BUT .....the signal can be lost along the way, that's why I suggested checking AT THE SENSOR first, then if ok there check at the DME. IF checking with Durametric, and NOT getting a signal that you command, you will need to go backwards to my first diagnostic routine, and check at the sensor last.. It can get confusing if not following routine in order because the results of each step dictate the direction to go next and why.

Hi, thank you, I will check with the Durametric first and if I do not get the expected response will move to the sensor. Then will report back. I am in the UK so that will be tomorrow for me. By the way, I was reading Scott's epic 996 engine rebuild thread and was wondering what the AOS device he fitted was. Now I know! Very nicely done! Thanks again Berni

If you determine that the sensors/wiring/fuses are good/operating properly (in other words, that the problem is definitely in the ECU/DME) You can have it repaired by ECU Doctors (or similar type service)... Good luck

Hi I connected up the durametric, got the gar to operating temperature and sprayed fuel (easy start) into the intake. Voltage behaviour as reported by the durametric as follows: Bank 1 0.47 volts, almost completely stable Bank 2 went straight up from a low of 0.11v (variable) to a high of 0.87v and stayed there for a few seconds before coming back down and fluctuating again. The heater showed about 1.07v on all 4 sensors. o2 sensor resistance as reported was a bit all over the place Bank 1 before CAT (the P0134 problem sensor) 16,320 Ohm Bank 1 after CAT 320 Ohm Bank 2 both 64 Ohm I did not get the chance to create a vacuum leak or get a wire connected to the sensor directly because I need to get under the car for that. I may try again later today. Many thanks Berni

Quotes source post: 16973095

Hi I was hoping to get a solution for less money if in fact it is the ECU. I can buy a secondhand set with a couple of remotes for GBP 300, which is the same money the ECU people want for a rebuild. I currently don't have a working remote, so it does make more sense to buy secondhand in that regard. I did take my DME apart again, but separated it from its backing this time and checked continuity from the pins B15 signal & B9 earth to the components on the board they connect to. It checked out and I could not see any damaged looking components even with a high power magnifier. So I am still not 100% what is wrong. Berni