What is "ASD" relay for?

[MJR]

Key off, send 12 volts to the ASD sense by splicing around the suspected problem area. Then key on. What could this harm? I worked on Jeeps for 8yrs. and while I didn't consider myself an electrical specialist I think that is a safe and proper method of finding the problem. What am I missing? And what changed after 96 that would change your advice?

Fuse #21 20A in the underhood fuse box is for the injectors and PCM ASD relay sense wires. If he unplugs the PCM connectors, turns the key on, and grounds pin #3 (K51 18DB/YL) in the gray connector the ASD relay should click on and you should see 12V at pin #12 (A142 18DG/OR) in the gray connector. If this checks out then for some reason the PCM is not turning it on like no crank sensor input.

I consider that some people need to be warned about jumpering wires if they are not sure about what they are doing as it can cause damage. The 96-up JTEC controllers are not as short tolerant as the previous SBEC controllers and even a momentary short can blow out a driver inside the controller necessitating a new controller.

 

[kst8engineer]

From the testing I've done, I believe the PCM is energizing the ASD relay (I measure 12V on the relay control terminal w/ignition on), so that would lead to believe that CPS signal is OK.

What I don't have is power to terminal 30 on the relay which is terminal C2 in the PDC. From what I'm seeing on Alldata's schematics, it looks like terminal C2 gets it's juice from fuse 19 (as Mike mentioned earlier), and then goes straight to the battery. I think my next course of action is to measure resistance between terminal C2 and terminal A17 (fuse 19's output) to see if there is a problem in the wiring within the PDC. I'm hoping that's it, because it's finally starting to make sense.

Thanks for all the great input, guys. I'm thinking the $25 Alldata subscription I signed up for this evening might be well worth the money! I'll keep you posted on the saga...

 

[MJR]

From the testing I've done, I believe the PCM is energizing the ASD relay (I measure 12V on the relay control terminal w/ignition on), so that would lead to believe that CPS signal is OK.

What I don't have is power to terminal 30 on the relay which is terminal C2 in the PDC. From what I'm seeing on Alldata's schematics, it looks like terminal C2 gets it's juice from fuse 19 (as Mike mentioned earlier), and then goes straight to the battery. I think my next course of action is to measure resistance between terminal C2 and terminal A17 (fuse 19's output) to see if there is a problem in the wiring within the PDC. I'm hoping that's it, because it's finally starting to make sense.

Thanks for all the great input, guys. I'm thinking the $25 Alldata subscription I signed up for this evening might be well worth the money! I'll keep you posted on the saga...

First the ignition switch through a fuse powers one side of the relay coil and the PCM grounds the other to turn it on. If you are not getting the ground when the engine cranked over then the PCM is not trying to turn on the ASD relay.

If you don't have battery power at the relay then that's what you need to track down then.

 

[explorer]

Fuse #21 20A in the underhood fuse box is for the injectors and PCM ASD relay sense wires. If he unplugs the PCM connectors, turns the key on, and grounds pin #3 (K51 18DB/YL) in the gray connector the ASD relay should click on and you should see 12V at pin #12 (A142 18DG/OR) in the gray connector. If this checks out then for some reason the PCM is not turning it on like no crank sensor input.

I consider that some people need to be warned about jumpering wires if they are not sure about what they are doing as it can cause damage. The 96-up JTEC controllers are not as short tolerant as the previous SBEC controllers and even a momentary short can blow out a driver inside the controller necessitating a new controller.

I think?? I understand what your saying. But is it not OK to send 12 volts to the proper pin if that is what is supposed to be there during operation? I'm looking at a 97 TJ manual as I recall diagnosing this. In my case, the S101 splice was where the problem was. Grounding pin #3 would turn the ASD on, there would be power through S101 to S128 which would feed the injectors, ignition, and O2, but S101 was not feeding power to the PCM's ASD sense circuit. The trouble shooting tree repeatedly led you to replace the PCM, but that was not the problem. I could verify 12V before and after S101 leading towards S128, but 1/2" down A142 going to the sense circuit, there was no power.

Sorry to get into this big discussion, but maybe it will help with the original post.

 

[MJR]

I think?? I understand what your saying. But is it not OK to send 12 volts to the proper pin if that is what is supposed to be there during operation? I'm looking at a 97 TJ manual as I recall diagnosing this. In my case, the S101 splice was where the problem was. Grounding pin #3 would turn the ASD on, there would be power through S101 to S128 which would feed the injectors, ignition, and O2, but S101 was not feeding power to the PCM's ASD sense circuit. The trouble shooting tree repeatedly led you to replace the PCM, but that was not the problem. I could verify 12V before and after S101 leading towards S128, but 1/2" down A142 going to the sense circuit, there was no power.

Sorry to get into this big discussion, but maybe it will help with the original post.

First I don't use the diagnostic books for the reason that they can lead you in the wrong direction. It is better to understand how it works. By going though the steps I listed above it will tell you if that wire is open. If the fuse for the injectors is open the PCM will not get the sensed feed either. It is important to note that this DTC can be set by pulling the ASD relay and switching the key to the on position. It is far safer when jumpering to unplug the PCM and feed a ground to the pin listed with the key on to see if the ASD relay comes on and you can then see if you have 12V at the sense pin. This is very easy to do and it checks all the wiring from the PCM and back.

 

[kst8engineer]

Guys, thanks a million for all your help! The Cherokee now runs for the first time since I've owned it! I bought it as a wrecked rebuilder about a month ago, but it had never run since I bought it...

I went to measure the resistance tonight between the ASD relay and fuse 19 (which I was guessing was one of the big relays closer to the front). I had already verified that all of the large relays were good and that all of them had power. When I looked at the diagrams to find fuse 19, I learned that it isn't one of the big ones, it's one of the little small ones between the large fuses and the relays. Sooooooo, when I looked for fuse 19, I found an empty fuse terminal -- the fuse was missing completely. Where it went and why it wasn't there, I haven't a clue. Nevertheless, after putting a 25A fuse into the proper location, she purrs like a kitten.

Thanks again!
Galen

 

[MJR]

Guys, thanks a million for all your help! The Cherokee now runs for the first time since I've owned it! I bought it as a wrecked rebuilder about a month ago, but it had never run since I bought it...

I went to measure the resistance tonight between the ASD relay and fuse 19 (which I was guessing was one of the big relays closer to the front). I had already verified that all of the large relays were good and that all of them had power. When I looked at the diagrams to find fuse 19, I learned that it isn't one of the big ones, it's one of the little small ones between the large fuses and the relays. Sooooooo, when I looked for fuse 19, I found an empty fuse terminal -- the fuse was missing completely. Where it went and why it wasn't there, I haven't a clue. Nevertheless, after putting a 25A fuse into the proper location, she purrs like a kitten.

Thanks again!
Galen

Glad you found it. With electrical stuff I have found the best place to start is by checking all the fuses and even putting some in open spots that have both terminals. I have found some problems that way.