Testing PCM (no crank)

[runs_with_waves]

Good morning everyone!

First time poster here. Loving this resource so far. Greatly appreciate the service manuals.

I have a No Crank condition.

So far, I have; Ignition Cylinder (Replaced), Ignition Switch (Replaced), Neutral Safety Switch (Bench Test - good), Starter Relay (Bench Test - Good), Starter Solenoid / Motor (Bench Test - Good), Power Dist. Relay (Replaced).

After digging through the Service Manual I have a nice list of 5v circuits to test (oh, joy!) that could cause the PCM to trip the ASD (not getting any signal to the ASD from the PCM), or just not function. I didn't find a testing procedure for the PCM itself in the service manual, so either I missed it in the 1678 pages, or it's not in there.

My initial search had me testing the Ignition Sense, and I was able to confirm 12v from the Neutral Safety Switch to the PCM (C3, Pin 21), but I am not getting enough Voltage out of C3 Pin 38 to close the Starter Relay circuit (Getting 31.5mV's w/ Key On and Key Start, 0.0v at Key Off, and 0.2 Ohms between Pin 38 and Relay).

Tonight I am going to test Ignition Switch to the PCM.

Any insight or direction would be greatly appreciated.

o7

 

[JKP]

If I remember correctly, the PCM on the 05 and 06 is involved in the actual cranking.

Did you verify the ignition actuator pin is good?

Mark @Wranglerfix is the person to contact if you narrow it down to the PCM.

 

[macleanflood]

Have you tried putting the key into the on position and jumping the starter solenoid?

-Mac

 

[runs_with_waves]

If I remember correctly, the PCM on the 05 and 06 is involved in the actual cranking.

Did you verify the ignition actuator pin is good?

Mark @Wranglerfix is the person to contact if you narrow it down to the PCM.

I disassembled the ignition while installing Ignition Switch, pin was not broken. And the ignition switch appears to function, as all obvious peripherals power up with the key in the Run position.

Going to be testing Ignition Switch outputs to the PCM tonight, if I have daylight after work.

 

[runs_with_waves]

Have you tried putting the key into the on position and jumping the starter solenoid?

-Mac

I jumped the Starter Relay's 10 awg wires to the solenoid as an initial test of the Solenoid/Starter. I have not jumped at the Solenoid with the Starter Relay in place.

Will try tonight.

 

[runs_with_waves]

Good morning everyone!

First time poster here. Loving this resource so far. Greatly appreciate the service manuals.

I have a No Crank condition.

So far, I have; Ignition Cylinder (Replaced), Ignition Switch (Replaced), Neutral Safety Switch (Bench Test - good), Starter Relay (Bench Test - Good), Starter Solenoid / Motor (Bench Test - Good), Power Dist. Relay (Replaced).

After digging through the Service Manual I have a nice list of 5v circuits to test (oh, joy!) that could cause the PCM to trip the ASD (not getting any signal to the ASD from the PCM), or just not function. I didn't find a testing procedure for the PCM itself in the service manual, so either I missed it in the 1678 pages, or it's not in there.

My initial search had me testing the Ignition Sense, and I was able to confirm 12v from the Neutral Safety Switch to the PCM (C3, Pin 21), but I am not getting enough Voltage out of C3 Pin 38 to close the Starter Relay circuit (Getting 31.5mV's w/ Key On and Key Start, 0.0v at Key Off, and 0.2 Ohms between Pin 38 and Relay).

Tonight I am going to test Ignition Switch to the PCM.

Any insight or direction would be greatly appreciated.

o7

Should also be noted that no DTC (error codes) were displayed prior to, during or after testing.

 

[runs_with_waves]

[Update] I was able to confirm Ground at Pin 38 on C3 with the key in the run position.

My next curiosity was continuity between the Ignition Switch and Starter Relay. Resistance was 14ohms, more than I would like to see. I believe these 14 ohms and the 75 at the relay may be enough to keep the relay from activating.

Tonight I will be doing some more trouble shooting around the harness plug for the ignition switch looking for low/no voltage.

 

[cpainter56]

Any updates?, I seem to have a similar issue

 

[macleanflood]

Any updates?, I seem to have a similar issue

Do you have RPM on the tach when it cranks?

-Mac

 

[cpainter56]

Yes, everything is normal, just have to crank it via jumping the relay. Thus the issue must be between the ignition switch (which is new, with a verified unbroken actuator pin) and the relay. The control wire at the relay is not receiving the 12 volts. This is on a 1997 or 1998 TJ.

 

[Rickyd]

Yes, everything is normal, just have to crank it via jumping the relay. Thus the issue must be between the ignition switch (which is new, with a verified unbroken actuator pin) and the relay. The control wire at the relay is not receiving the 12 volts. This is on a 1997 or 1998 TJ.

Just because the actuator isn't in pieces doesn't mean it isn't worn or tweaked enough to not function. That was the case on my 97. Will a screwdriver turning the electrical switch start it?

 

[cpainter56]

Actuator is verified good, the wire going to the relay is not providing the 12 volts to trigger the relay when the key is turned to the start position.

 

[CharlesHS]

Verify all wiring jumpers and wiring connector pins on the trigger wire circuit are clean and not loose.

 

[cpainter56]

Anyone got a good diagram of those circuits? I’m looking for my fsm files

 

[CharlesHS]

CJPainter,

The FSM for your 2002 TJ is provided in the Jeep Wrangler TJ Resources section.
Download the PDF of the FSM and look a the Electrical Section 8W-21-1 for the Starting Circuit.

 

[Rickyd]

Actuator is verified good, the wire going to the relay is not providing the 12 volts to trigger the relay when the key is turned to the start position.

You unplugged the connector on the ignition electrical switch and verified the power wire to the connector has power? You verified with an ohm meter that the actuator is making the switch send power to the relay on start? You verified the power makes it through the clutch or neutral safety switch? It isn't a complicated circuit