It just never ends. 98 Mazda 626 GF 2L. It cranks great, but there's no spark at any of the plugs and I can't connect to the ECU. Coil pack is new, I've driven it maybe five times since I replaced it. I've also been having a low voltage from the alternator for a while, about 13.75v, but can't so far find any problem with the alternator.

I'm kinda freakin out, thinking maybe the ECU has given up the ghost.

This is somewhere between a rant and wanting to have someone tell me that's it's likely not an ECU problem... arg!!!

I know I need to check the pins coming into the coil from the ecu to see if a signal is coming in or not... just afraid of what the results will be...

EDIT May 31st, 2016

So I go out today to try and make some progress on this problem, and what happens? The car starts right up and I am able to connect to the ECU / PCM with no problem.

When I connected I got a 0113 DTC. I had this error a few months ago, but I cleared it and it didn't come back. This time I cleared it, ran a KOEO test and it came back. Cleared it and ran a KOER test and it came back. This is the list of causes ( also for a few other DTCs ):

enter image description here

So I went to look at the IAT connector and found this:

enter image description here

The wire seems to be made of four strands, two of which are broken and probably making intermittent contact.

I'm going to go look for a good connector from a junk yard and splice it in, however, I'm not sure this is really the source of the problem for a few reasons. If I completely disconnect the IAT sensor the car starts up just fine, so I don't think that frayed wire would cause an intermittent ECU problem, would it? Looking at "Cranks Normally But Will Not Start" in the troubleshooting section of the WSM it does mention a few problems where a short to ground can be a cause, like with VREF and an "IG" line from the DLC, but I don't have a short to ground here, I've got a partial open.

The other thing that's making me suspicious is an aftermarket keypad immobilizer that's been installed in addition to the factory key chip immobilizer. I remember the previous owner saying he had disabled it because it had been causing him problems, however it is still physically wired into the system under the dash ( it's a nasty rat's nest of spliced wires under there ) and I'm wondering if maybe it's haunting me from the grave so to speak.

I'm still feeling like this might be related to the alternator problem since I think the voltage regulation on this model is done by the ECU.

EDIT June 2nd, 2016

So I spliced in the new IAT connector, cleared the codes, ran the KOEO and KOER self tests, and so far so good. Not sure what to make of it. I was thinking of pulling the ECU out to visually inspect it, but maybe I'll just keep an eye on things in the mean time and see what happens.

  • I would recommend checking all the powers and groudns at the PCM. Then look at the cranks shaft position sensor.
    – vini_i
    May 29, 2016 at 20:04
  • Is there a cam shaft or crankshaft position sensor to check? How about voltage at the ECU? May 29, 2016 at 20:18
  • @Pᴀᴜʟsᴛᴇʀ2 There are both cam and crank sensors. I have to look up where to check voltage at the ECU. May 29, 2016 at 21:06
  • check the fuses before checking pulling down the ecu. maybe one is blown.
    – Ben
    May 29, 2016 at 21:10
  • Timing belt? What prompted you to do the initial work to the vehicle?
    – sntnmjones
    May 30, 2016 at 0:06

2 Answers 2


So basically, the problem was shorted out wires in the Cobra alarm system which were causing the alarm system to randomly disconnect the ECU, fuel pump, etc:

enter image description here

I'm not going to copy the full answer here, you can read it over on this other question.


The break in the wire could have possibly been causing a spike which was scrambling the ECU. I suspect that the problem won't occur anymore since you've changed that bit of loom.

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