PCM Dead?

[SteveCsTJ]

H, new to the forum.

Have a 2003 TJ 2.4L 5 speed. Having issue where it cranks but won’t start. Cluster comes on but gauges don’t work (ie battery volts stays at bottom , etc).

Had driven great, brought to a shade tree mechanic who was checking why the AC wasn’t working and was probing the fuse box and now no go.

Checked fuses and relays - all good.

OBD connector with SnapOn tool says “no communication “.

Any ideas on what to check next? Is the PCM fried?

Thanks.

 

[Obi-Wan]

Is the odometer displaying any error messages such as "no bus"?

Also, have you tried pulling any codes using the trip/reset method?

 

[SteveCsTJ]

Is the odometer displaying any error messages such as "no bus"?

Also, have you tried pulling any codes using the trip/reset method?

@Obi-Wan - the odometer displays the mileage, no messages.

I’m not familiar with the trip/reset method, although I did disconnect the battery for a while to see if that would reset things, to no avail.

 

[Obi-Wan]

I’m not familiar with the trip/reset method,

No problem. Here's how you do it.

With the ignition in the off position, quickly cycle the key from OFF to ON three times, leaving the key in the ON position in the last cycle.

If any P-codes are present, they will display within the odometer.

Here's a video demonstrating it if you need a visual.

If this doesn't net any results. We'll grab a multimeter and start checking a few points for power. Specifically at the OBD2 port.

 

[SteveCsTJ]

No problem. Here's how you do it.

With the ignition in the off position, quickly cycle the key from OFF to ON three times, leaving the key in the ON position in the last cycle.

If any P-codes are present, they will display within the odometer.

Here's a video demonstrating it if you need a visual.

If this doesn't net any results. We'll grab a multimeter and start checking a few points for power. Specifically at the OBD2 port.

Ok tried so many things but still no results. I did wind up getting a new PCM from wranglerfix as old unit had a scorched chip when I opened it. After install still not working - cranks but no start and gauges (Volts, etc) still not coming up .

After some research checked the pins 22 and 2 for power with the key on, on the black connector for the pcm. Pin 22 has 12v but nothing coming from Pin 2 . From what I read this is supposed to have 12v when key on (think I saw this described as fused ignition output.

Are those the correct pins to be checking to see if the pcm is getting power? If so, any ideas to check since pin 2 has no power?

Fell like there’s a short somewhere.

 

[AndyG]

@Wranglerfix Is based out of Florida and if you have a PCM Issue I cannot think of anyone better- the @ symbol will send him a notification that he has been mentioned. It makes his ears burn.

I think if you’ll take the time to talk to him you’ll be glad you did.

 

[SteveCsTJ]

@Wranglerfix Is based out of Florida and if you have a PCM Issue I cannot think of anyone better- the @ symbol will send him a notification that he has been mentioned. It makes his ears burn.

I think if you’ll take the time to talk to him you’ll be glad you did.

Yep. He’s a good guy. As mentioned above I ordered a unit from him.

Trying to figure out the wiring to the PCM though as mentioned above . Any help would be appreciated.

Was trying to trace the pin # 2 wire back towards ignition if that’s indeed where it’s sourced but couldn’t find it. Even have the alldata wiring diagram but it shows it going to the transmission control module which I wouldn’t assume I even have since it’s a manual.

@Obi-Wan