Great to hear that you found it. In my case, it turned out to be the PCM. I’ll write a concluding post about it after this.
Cranks-no-start after battery drain
- Thread starter Marty123
- Start date
Great to hear that you found it. In my case, it turned out to be the PCM. I’ll write a concluding post about it after this.
I thought I’d write a final update now that I’ve finally got the Jeep running again.
I went through quite a few stages during the troubleshooting process. Among other things, I converted the alternator setup to use an external voltage regulator and installed one. After that, the engine ran fine for about 10 minutes, then stalled a couple of times, and eventually went completely dead. It would no longer boot up properly.
A 10A fuse kept blowing, but I noticed that it did not blow when the PCM was disconnected. I then removed and opened up the PCM, and found a couple of obviously burnt chips/resistors on the board.
After that I tried to figure out whether it could be repaired cheaply, but in the end I decided to order a replacement PCM from a company in the US called Drivetech, which I found on eBay. It was a refurbished PCM, programmed for my Jeep model and with my VIN.
It arrived here in Sweden after about two weeks, and after paying VAT and customs fees, I finally had the “new” PCM in my hands.
Did I install and test it without being 100% sure that there wasn’t still an underlying issue, such as a short in the wiring harness? Yes, I did.
And the Jeep started right up.
At first, both the check engine light and the battery light were on, but they went out gradually after a few starts/drives.
So, in summary: the root cause in my case was the PCM. It is still possible that a failed alternator damaged the PCM in the first place, but that part remains a bit unclear.
For now, the Jeep is running beautifully again.
Feel free to ask if you have any questions — there’s plenty more to tell.
I went through quite a few stages during the troubleshooting process. Among other things, I converted the alternator setup to use an external voltage regulator and installed one. After that, the engine ran fine for about 10 minutes, then stalled a couple of times, and eventually went completely dead. It would no longer boot up properly.
A 10A fuse kept blowing, but I noticed that it did not blow when the PCM was disconnected. I then removed and opened up the PCM, and found a couple of obviously burnt chips/resistors on the board.
After that I tried to figure out whether it could be repaired cheaply, but in the end I decided to order a replacement PCM from a company in the US called Drivetech, which I found on eBay. It was a refurbished PCM, programmed for my Jeep model and with my VIN.
It arrived here in Sweden after about two weeks, and after paying VAT and customs fees, I finally had the “new” PCM in my hands.
Did I install and test it without being 100% sure that there wasn’t still an underlying issue, such as a short in the wiring harness? Yes, I did.
And the Jeep started right up.
At first, both the check engine light and the battery light were on, but they went out gradually after a few starts/drives.
So, in summary: the root cause in my case was the PCM. It is still possible that a failed alternator damaged the PCM in the first place, but that part remains a bit unclear.
For now, the Jeep is running beautifully again.
Feel free to ask if you have any questions — there’s plenty more to tell.
The other day the battery light on my JK 2011 3.8 came on while on the highway. I tried to push on home but after 10 mins all hell broke loose. All lights startred blinking and 10 secs later the engine died and I pulled to the side. Had to order tow service to parking lot. Then from there my friend helped me flat tow to my home. I'm guessing alternator failure but haven't gotten to that yet since the engine wont start efter new battery (the old one needed changing anyway)
Some facts:
- cranks healthy but no start
- no spark
- no power to ignition coil (it seems - but maybe when cranking - can't check)
- no codes. either with ODB2 or manual check
- ODB2 presents VIN so communicates with PCM
- OD/off light is lit and can't be turned off with button
- ESP light is lit (skidding car symbol)
- grounds are ok (the ones I could find/get to)
- checked all fuses, they look good
- switched around relays - no effect
- I can hear whirring 2-3 secs when connecting battery - fuel pumps ok?
- removed and opened PCM. Doesnt look burned or faulty to the eye
- all electricity seem to be working inside car, gauges working
- fuel in tank
- tried starting in P and in N, no difference
Please advice
-
If the "battery light" came on while driving, test your alternator. The only time your battery is actually draining during normal operation is when starting. I had this happen to me twice over the years with different vehicles, and both times the alternator had expired. Normally the battery is simply in the circuit, but there should be no draw on it unless the alternator is not providing current.