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Random Starting Issues - ECU / PCM Problem?


NAXJA Forum User
Dallas, Tx
My '99 XJ has recently given me issues randomly not starting. I thought at first it was a starter issue (although I had a new starter already installed only 2 years ago). I had the starter replaced again. That seemed to fix the problem. However, not long after that, I drove it on a short local trip and turned off the ignition. When I got back in maybe 10 minutes later and tried to start it, I got no response. I had it towed to the same shop that replaced the starter. When they went to check it, the car actually started fine. I brought it back home and drove it without issue for a few weeks. But then I experienced the same issue. I drove it. Turned it off. Got back in and had no ignition response.

There is no check engine light on.

My thoughts are this could be an ECU / PCM going bad. Or possibly a wiring issue.

Anyone else experienced this same issue and found a solve?
Most common is a problem is the park/neutral switch interlock on the trans. Next time try slightly moving the shifter and also try it in neutral!
Diagnostics are necessary to avoid expensive shotgunning of random parts.

The park/neutral switch interlock or Neutral Safety Switch (NSS), is a logical suspect. Starting/Charging wiring problems is another common problem. Ignition switch problems are much less common, but do occur.

PCM/ECM failure is very uncommon and should only be considered after thorough and in-depth diagnostics and trouble shooting of the more common and more logical malfunctions.

Common wiring problems:

• dirty, corroded, damaged, or loose battery terminal or wire connections
• internally corroded battery wires
• a short circuit or parasitic drain
• a failing battery
• a failing alternator
• leaving the lights on

Perform routine maintenance of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Battery terminals and battery wire connectors should bright silver, not dull gray/black and corroded. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, wire brush, and clean until shiny the cable/wire ends and whatever they bolt onto.

Jeeps do not tolerate low voltage, bad wire connections, or poor grounds.
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Incidentally, if the shop says you don't have an NSS, ask it they think if has a "Prindle" switch".

Funny story: Had a dealer once tell me my XJ had one of those and not an NSS when I had it in for an NSS replacement because the backup lights didn't come on in reverse. Didn't figure it out until I got the invoice and found they'd spelled it "PRNDL", LOL. It was still the NSS they replaced to get the lights working, though.
Could also be a broken ignition tumbler. The tab can break off the back and can intermittently still catch. I go through more tumblers than starters, but most people don't have to stop and start theirs 20-50 times a day.
The service manual and the parts diagram for the later models calls it the PRNDL switch. It can usually be cleaned up and refurbished, assuming you get it off in one piece. At the dealers labor rates though, a new one might be cheaper.
The service manual and the parts diagram for the later models calls it the PRNDL switch.

Really? And all these years I thought that the service writer was either "feeding me a line" or assuming I was one of those "car is an appliance" idiots that forget to have the oil changed. At the time, when I got the invoice (I picked up the XJ that night after service hours from the receptionist in the showroom, and when I realized what the service writer meant when I talked to him on the phone (although, he could have just said "we call the NSS the PRNDL switch now"). Felt like I'd just been sold blinker fluid or muffler bearings....

I wonder what prompted the change (hopefully not the type of owners who'd think they had a "710 cap" if the oil cap was put on "upside down")...
Okay, so the problem ended up being pretty straightforward. The negative battery terminal clamp is cracked. Therefore, when I would tighten the nut down all the way there was still some wiggle with the negative terminal on the post. I wedged a small nail down in between the post and the terminal with a couple taps of a hammer on the nail and she started up. That's a temporary trick my neighbor taught me years ago. I've got a new set of cables and terminal clamps ordered from JeepCables.com.

I did take off the NSS (neutral safety switch) and gave that a good cleaning, so at least that project is done. I also ordered an ignition switch and actuator pin, but I'll hold off on installing those for now as that wasn't the problem.

Thanks to everyone for their help.
I always start with the basic diagnostics, checking for fuel and 12 volts in the right places. I wiggle, look at, poke at, and check fuses, wire connections, and wires looking for anything loose, unplugged, melted, corroded or otherwise damaged.
Here is my complete follow up for future readers.

The real problem ended up being a bad starter. I didn't think to test the starter because it had been replaced only 3 months earlier. However, after cleaning the NSS, changing all the battery cables, testing all the grounds and replacing the 3 components of the ignition (switch, actuator pin and cylinder lock) I decided to remove the starter and take it to the auto parts store for a full test. Turns out it didn't have enough solenoid pull current amps. After replacing the bad refurb starter with a new one, everything started normally. All is good...for now.

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Good to see that it was a relatively simple problem to solve, but maybe not so easy to find.

Recent repairs or modifications are always a good suspect when new problems appear. Never assume any replaced parts are trustworthy and functioning correctly. A guy at work has a part-time job at one of the big name auto parts chains, and he says a significant percent of their rebuilt starters and alternators are defective, or simply DOA right out of the box.
Yep, I completely believe that. I will know for the next time not to assume anything. Thanks!

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