dollar7499

1999 911 C2 Cab - I have been researching a P1531- the engine changes it's sound when I apply a 9v battery to the Variocam solenoid, so I opened the ECU and found a burnt transistor- but it's on the outside row of transistors and I haven't seen that in images yet.

Paul Waterloo

That's pretty cool. I don't know what you mean by "I haven't seen that in images yet"....but I would not be surprised if you found your issue.

I did look up the transistor number on ebay and found two hits. I don't know what the second two lines are.

https://www.ebay.com/itm/12331517862...Bk9SR6TlpoCnYw

https://www.ebay.com/itm/25320492557...Bk9SR6TlpoCnYw

DBJoe996

If you have no skill set to repair, I recommend getting your ECU to https://www.ecudoctors.com/#

dollar7499

The images I have seen for burnt transistors are normally on the inside of that heatsink. This one being on the outside makes me wonder if it's not the bank1 variocam solenoid signal. I ordered the transistor specified in other threads, $20 shipped but hopefully here quick as the sender is a hour from me. I was not able to test voltage at the solenoid as the connector is too short to get leads into from the wheel housing. But if the Durametric trigger doesn't work and a 9V battery does, it must be the ECU or the wire from ECU to the solenoid. Maybe 1999 ECUs were different than the other threads.

dollar7499

I am an electronics tech turned data analyst, I've re soldered transistors on MLPCBs before.

dollar7499

I may have found my own answer, the photos I have seen appear to be for bank2, and I am chasing bank1- I will trace the transistors to the pins and reference a pinout - pin 52 - Camshaft adjustment, bank 1, pin 25 - Camshaft adjustment, bank 2

Porschetech3

I think your testing method is flawed and inconclusive, but your visual inspection of the DME confirms a bad transistor...( probably from a shorted vario-cam solenoid on bank 1 or bank 2).

Both solenoids share a common 12v power lead, but have separate ground (-) leads to bank 1 and bank 2 solenoids and individual testing is necessary to determine which one is/was shorted..( caution: it can be an intermittent short and not show up at certain temps)

dollar7499

I did see solenoid continuity and resistance of 16.5ohms, trying to find out if that is out of spec range (I found nominal is 13.5). If that is out of spec, I don't want to fry the new transistor as well, please let me know a better way to determine a shorted solenoid.

Porschetech3

The nominal spec is 13 ohms ( less than 1 amp) and your reading of 16.5 ohms is even less amps ( and will not blow a transistor ) but you probably have an intermittent short occurring only at engine temps of ~ 200F.....You could perform the test again and heat the solenoids slowly to 250F ( with a heat gun) and watch the ohms reading to see if the short occurs ( like down to 1-5 ohms) when the temps are high..

Or as an alternative, you could install 2 2amp fuses in-line on the ground leads of each solenoid to protect the DME and also show you the faulty solenoid ..( when the fuse blows)...

Mike Murphy

I went through a P1531 code, failed solenoid, and then a failed/burned DME as well. That transistor failure came with a 2nd solenoid failure on the other side (P1530).

I agree that the problem with the shorts is:

1) The shared ground
2) An intermittent failure

I ended up having ECU doctors fix the 5.2 Motronic ECU (I have a 99 also), and had a shop replace the failed solenoids. They also replaced the tensioner pads, top and bottom, both sides, as I had brown debris in the oil filter and my cam deviations were -4 and -2.

That was maybe 3-4 years ago, and the car has been great ever since.

EDIT: pic of my failed transistor

dollar7499

That is a fantastic idea! I will install 2A fuses in the solenoid negatives.

dollar7499

I have installed the transistor and 2A ground fuses in the brown wire at the solenoid, bank1 now actuates through Durametric and the 1531 has not come back on some good drives, thanks everyone! I will update when the fuse blows and the code comes back.

Mike Murphy

That’s great. I assume you already repaired the DME?

dollar7499

Yup, soldered in the new transistor and have now gone ~20 miles without incident. The car doesn't seem any different with Vario working again. Not sure what I expected, I bought it with this issue

Mike Murphy

Interesting. My guess is that the Variocam being suck open/on behaves differently than stuck closed/off. And having one side working while the other side is not makes a difference as well.