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ASD Relay quiz

Old 07-03-2012, 04:13 PM
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Default ASD Relay quiz

I've read alot about faulty ASD relays but I'm looking to know what will cause an ASD realy to function (or not). Meaning, when an ASD realy prevents a vehicle from starting, what would be some of the root causes/symptoms that would tell the ECM to not engage the relay?

Again, to clearify, I'm not asking how to test the relay itself or the wiring to it. I'm asking what would have to be worng with the jeep to make the ASD relay prevent the Jeep from starting.
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Old 07-03-2012, 09:27 PM
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That's what I thought, no one has a clue.
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Old 07-03-2012, 09:31 PM
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Automatic Shutdown Relay

I've seen it tripped due to several reasons.

On my 96 ZJ, part of the wiring harness that wraps around the exhaust manifold, and melted the wire to the exhaust, causing a short, thus tripping the ASD.

I've also seen bad ignition trip an ASD code, but not necessarily the ASD circuit.

At startup, you have key cycles. The PCM sends out a certain voltage to every sensor, then looks for a signal back. If it does not see the correct voltage in an extreme case, (ie sends out 2.5v, expects 2.5 back, sees 0v or 5v) the PCM itself will trip the ASD circuit to prevent damage.

Thats to the best of my understanding and interaction with it.
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Old 07-03-2012, 11:41 PM
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Old 07-03-2012, 11:44 PM
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Originally Posted by Cherockee View Post
That's what I thought, no one has a clue.
they do but your not here so you missed it...lol...
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Old 07-04-2012, 07:56 AM
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Okay, still no real difinitive answer. How about this: If the oil pressure sender wiring is faulty or the sender is not working, cauisng a "check gauges" light, would that be enough to cause a the ASD relay stall the vehicle or prevent it from starting?
Would low voltage (but still enough for a slow crank) cause the relay to prevent starting?
Would a non working rear O2 sensor cause a either a stall or no start via the ASD realy?
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Old 07-04-2012, 03:21 PM
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Originally Posted by Cherockee View Post
Okay, still no real difinitive answer. How about this: If the oil pressure sender wiring is faulty or the sender is not working, cauisng a "check gauges" light, would that be enough to cause a the ASD relay stall the vehicle or prevent it from starting?
Would low voltage (but still enough for a slow crank) cause the relay to prevent starting?
Would a non working rear O2 sensor cause a either a stall or no start via the ASD realy?
The Allpar page is about as close as you'll come to the factory explanation. It was written by former Chrysler staff.

Doubtful it will shut down on low oil pressure or missing O2 sensor. I can unplug my oil pressure sender causing the gauge to read zero # , and have temporarily removed the rear O2 sensor while doing exhaust work. Jeep still runs under those conditions. I haven't found a way to trip the ASD relay yet.

It's original purpose was to shut off fuel and spark when the crank stops turning to prevent fires around a failed engine. That may well still be all it does.
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Old 07-04-2012, 03:55 PM
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Originally Posted by Cherockee View Post
Okay, still no real difinitive answer. How about this: If the oil pressure sender wiring is faulty or the sender is not working, cauisng a "check gauges" light, would that be enough to cause a the ASD relay stall the vehicle or prevent it from starting?
Would low voltage (but still enough for a slow crank) cause the relay to prevent starting?
Would a non working rear O2 sensor cause a either a stall or no start via the ASD realy?
i know if the harness makes short to ground it blows a fuse in under hood dc causing poweer to be cut of to asd
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Old 07-04-2012, 04:04 PM
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On YOUR CPS, I recently found this link on testing the , OBD II CPS, which may well apply to yours. I haven't tried it, don't know anyone who has. It looks like he's verifying .3? volt, AC, (with a true RMS meter), (back-probing, with it connected), at his third (Red) wire. (not the ground, and not the 5V-DC sensor feed). Aw geez. I just realized, THAT"S WITH IT RUNNING.. .35I don't know what % difference I would expect from my "cheap-o-meter", as opposed to the true RMS, but it might not be much. (about 7 minutes into the first Vid, IIRC) http://www.cherokeetech.com/VBull/sh...agnosis-Videos

Last edited by DFlintstone; 07-04-2012 at 04:11 PM.
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