OBD2 ABA intermittent no-start, ECU light not coming on

[Patrick007]

I just started having intermittent starting issues on my 98 ABA OBD2 motor (170k miles). At first this issue happened like once a month, now it's happening just about every time I drive the car. I turn the key to run, and IF the CEL comes on, the car will start right up. If the CEL does NOT come on, the car will not start. If I sit patiently for a few minutes and keep cycling the key on/off, eventually the ECU light will come on, and the car will start. I have verified during the no-start scenario that there is no spark. I believe the lack of an ECU light means the ECU is not powering up. As of recently, while driving, sometimes the car will lose power for a split second. The ECU light will come on for a couple seconds, then turn off again, and the car will continue to run. In this case it seems like the ECU is losing power for a split second, then coming back on. There are no stored codes. To me this screams of a failing relay, but apparently OBD2 cars do not have relay 109 (in position 3 per Bently). What controls power to the ECU on OBD2 cars? Is the relay on-board the ECU? I hope not Thanks for helping!

-Patrick

[greyhare]

Check fuse 15 and ignition switch terminal 6.

[bluntman220]

Bump Iam having this exact issue anyone solve this was it the BFI chip????? Help

[Anony00GT]

Read above your post. Check all fuses and ignition switch.

[bluntman220]

So the ignition switch itself could cause this issue I have already switched relay 109 cleaned all grounds , new batt and I have yet to swap the stck chip back in and do the ignition switch ( if that can cause this issue)

[Anony00GT]

Yes a bad ignition switch can cut off power to the ECU.

[jlsgli89-03]

check the Ignition switch or the Crank sensor

[Patrick007]

Hi everyone, sorry to drag this thread back from the dead. I didn't use the car for about a year, but I want to get it back on the road again, and obviously the problem didn't fix itself. The original post has the full description of the issue. I'm going to go outside now and test the ignition switch. Which terminals should have +12V when the key is on? If it looks like the ignition switch is good, which pin at the ECU should get +12V when I turn the key on? Could a bad aftermarket chip cause this problem? I will try swapping chips just to be sure... Any help would be greatly appreciated, thank you!

-Patrick

**Update**

Fuse (15?) marked Engine Electronics has 0V at both terminals when the ignition switch is off, and has +12V at the lower terminal when the ignition switch is on. This leads me to believe that the ignition switch is functioning properly and is switching power to the ECU. I will now swap chips to see if that's the issue. I may also kick and bang on the ECU in frustration to see if that works

[Anony00GT]

Check for power directly at the ECU, not the fuse.

According to your original post, this is an intermittent issue. You need to check power when the CEL is not illuminating during bulb check.

The answers to your questions about terminals and pins can be found in the appropriate service manual.

[Patrick007]

Thanks for the reply. This is a continuous issue now (but started as intermittent). I would love to check for power at the ECU, but I'm a lowly mechanical engineer and seriously cannot make sense of the Bentley wiring diagrams. I'm looking in the Engine Electronics section (97-391 in my book), I have found T68 (68 pin ECU connector) but cannot understand what pin supplies power to the ECU.

**Update**

Changed from the BFI chip to GIAC, and it fired right up...