Won't start

[TurboTJ]

Rubicon has been running perfectly for a long time. I went to the store today and when I tried to start the engine all the panel lights came on but nothing from the starter. No clicking or sound of any kind, and the lights did not dim. I believe the battery is good but I will verify that. I flat-towed the Jeep home and jump started it while towing. It started immediately. So I assume I just have a bad starter. Any other opinions? Is there a relay that controls the solenoid that might have gone bad?

 

[TurboTJ]

Well, it appears I have a real problem. The battery is good, the starter is good, the start relay in the PDC is good, the clutch interlock switch is good and no fuses are blown. Whereas the engine did at first start and run when towed, now it will no longer. I can manually crank the engine by bypassing the start relay in the PDC but no start. As I see it, the only thing left is the PCM. Any other suggestions?

 

[Daryl]

Check your ignition switch actuator.

 

[TurboTJ]

It doesn't help that the wiring manual appears to have errors in it. On page 8W-10-12 it shows the engine starter motor relay (in the PDC) in a normally closed position. On page 8W-21-3 it shows it in a normally open position, which would seem to be the logical position. The actual relay when measured is normally open, and when activated it closes. The relay coil is connected between the start terminals on the ignition switch and the "starter motor relay control" on the PCU. The ignition switch start terminal supplies 12V and presumably the PCU switches the other side to ground. Neither of these things happen. Neither relay coil terminal goes to 12V or is switched to ground.

 

[TimmiT]

Crankshaft sensor? Not the camshaft in the distributor, but down st the transmission. Was reading these will not run without a signal from there. New to jeeps, though.

 

[NskLJ]

It doesn't help that the wiring manual appears to have errors in it. On page 8W-10-12 it shows the engine starter motor relay (in the PDC) in a normally closed position. On page 8W-21-3 it shows it in a normally open position, which would seem to be the logical position. The actual relay when measured is normally open, and when activated it closes. The relay coil is connected between the start terminals on the ignition switch and the "starter motor relay control" on the PCU. The ignition switch start terminal supplies 12V and presumably the PCU switches the other side to ground. Neither of these things happen. Neither relay coil terminal goes to 12V or is switched to ground.

The relay on page 8w-21-3 is correct. The diagram on 8w-10-12 the wire should go to the normally open terminal. Check for 12 volts at the b5 terminal trace that down. Pink/orange wire at the ignition switch.

 

[TurboTJ]

The relay on page 8w-21-3 is correct. The diagram on 8w-10-12 the wire should go to the normally open terminal. Check for 12 volts at the b5 terminal trace that down. Pink/orange wire at the ignition switch.

Thanks! I figured the drawing was wrong but thought I might be missing something.

I cannot tell which terminal on the relay is B5 because the pin numbers on the relay do not match the numbers on the schematic. The two coil terminals on the relay are pins 1 and 2. The normally open contacts are pins 3 and 5. This is exactly opposite the schematic. There is no voltage on either of the coil terminals when the ignition switch is held in the start position. I do not know which is which but it doesn't matter, no voltage is coming from the ignition switch as pages 8W-10-11 and 8W-21-3 indicate it should. I will trace the wire out to the ignition switch next. BTW, the fuse (fuse 22 in the PDC) that feeds the start terminal on the ignition switch (pin 6) checks out good.

But that might only solve part of the problem. I can get the starter to crank if I jumper across the relay with the ignition switch on, but it won't run now. Previously it did run after I towed the jeep to start it. Now it won't run at all. I don't know how I could have made things worse but I apparently did.

Edit: I figured out the relay pin numbers from the drawing of the PDC on page 8W-10-2. The schematic B1 is relay pin 3, schematic B2 is relay pin 5, schematic B3 is relay pin 1 and schematic B5 is relay pin 2. From this I can tell the position of B5 in the PDC that should be receiving voltage from the ignition switch, which it is not.

 

[NskLJ]

Thanks! I figured the drawing was wrong but thought I might be missing something.

I cannot tell which terminal on the relay is B5 because the pin numbers on the relay do not match the numbers on the schematic. The two coil terminals on the relay are pins 1 and 2. The normally open contacts are pins 3 and 5. This is exactly opposite the schematic. There is no voltage on either of the coil terminals when the ignition switch is held in the start position. I do not know which is which but it doesn't matter, no voltage is coming from the ignition switch as pages 8W-10-11 and 8W-21-3 indicate it should. I will trace the wire out to the ignition switch next. BTW, the fuse (fuse 22 in the PDC) that feeds the start terminal on the ignition switch (pin 6) checks out good.

But that might only solve part of the problem. I can get the starter to crank if I jumper across the relay with the ignition switch on, but it won't run now. Previously it did run after I towed the jeep to start it. Now it won't run at all. I don't know how I could have made things worse but I apparently did.

Edit: I figured out the relay pin numbers from the drawing of the PDC on page 8W-10-2. The schematic B1 is relay pin 3, schematic B2 is relay pin 5, schematic B3 is relay pin 1 and schematic B5 is relay pin 2. From this I can tell the position of B5 in the PDC that should be receiving voltage from the ignition switch, which it is not.

Relay pin locations are pretty standard. If it is the standard Bosch relay ( 1” x 1”) the two terminals that are parallel are #85 & #86 ( Bosch designation) these are the coil terminals. If it is the one of smaller relays you can find the pin designations on line. ( I don’t know them in my head) Test the ignition switch and power feed to it. The ignition switch is held on with tamper proof torx screws so you will need one of those. You can pick up a cheap set of screw driver bits that will work.

 

[TurboTJ]

The relay pin designations 1, 2, 3 and 5 map to the PDC terminals B3, B5, B1 and B2, respectively. There is a pin 4 on the relay which is the NC pin and that goes into a unmarked slot in the PDC that has no contact. So I’ve figured that all out and assuming pages 8W-10-11 and 8W-21-3 are correct, I know what voltages should be on which pins during start…… 12V on B5 from the ignition switch and ground on B3 from the PCU. Neither of those conditions are met.

As far as removing the ignition switch, are they just standard Torx screws or is there a special anti-tamper version I need tools for?

 

[NskLJ]

The relay pin designations 1, 2, 3 and 5 map to the PDC terminals B3, B5, B1 and B2, respectively. There is a pin 4 on the relay which is the NC pin and that goes into a unmarked slot in the PDC that has no contact. So I’ve figured that all out and assuming pages 8W-10-11 and 8W-21-3 are correct, I know what voltages should be on which pins during start…… 12V on B5 from the ignition switch and ground on B3 from the PCU. Neither of those conditions are met.

As far as removing the ignition switch, are they just standard Torx screws or is there a special anti-tamper version I need tools for?

They are the tamper proof torx. I just had to put an ignition actuator in my Jeep.
https://www.harborfreight.com/secur...MIs9Xf-Yj9gAMVogh9Ch1SUAhyEAQYASABEgJ3j_D_BwE

 

[TurboTJ]

Thank you all for your help. Daryl first identified the problem but I was so sure I had fried the PCU that I dismissed that. Blaine got me back on the right track by suggesting I do the simple things first, step by step, before leaping to conclusions. Ultimately when I removed the ignition switch from the ignition lock assembly I found that I could start and run the engine by manually actuating it. It was just the broken actuator afterall.

 

[mrblaine]

Thank you all for your help. Daryl first identified the problem but I was so sure I had fried the PCU that I dismissed that. Blaine got me back on the right track by suggesting I do the simple things first, step by step, before leaping to conclusions. Ultimately when I removed the ignition switch from the ignition lock assembly I found that I could start and run the engine by manually actuating it. It was just the broken actuator afterall.

Always when we encounter things like this that seem very complicated and difficult to troubleshoot, start with the basics. Even if you think you know something is good, verify it as known good. We have had folks bring us their problem child they have spent 50 hours + on troubleshooting a "died on the trail" and won't crank or start. Start with the basics, get out the test light and probe the fuses behind the glove box, find the blown ASD fuse, pop a new one in, fires right up.

Don't pull the fuses that have the little terminal extensions that stick through the plastic on top. Put a test light on both and verify they are good that way. Trust, but verify and only after should one start down the rabbit hole of the complicated stuff.