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ASD relay doesn't pull over - '96 XJ 4l Petrol - no fault codes

A

adam_q

NAXJA Forum User
Location
UK
I have a problem that the PCM isn't grounding the ASD relay so it isn't pulling over - so no spark etc. And it won't start of course.

I checked for fault codes on the Engine Warning light - I have a "12" then a "55", the 12 means I disconnected the battery, which I did after the fault appeared so I could check the PCM connections through the loom to the ASD.

THe ASD winding ground line is intact all the way to C3 on the PCM plug so that's not the problem.

Any ideas? I have a list or around 24 things to try in the service manual but I suspect the PCM might be snafu. Some of this list must be covered my the fact that there's no fault code.

Even if I ground the ASD line to get spark it still won't run.
 
Incidentally if you search for "ASD" in the forums it finds nothing - which is plainly wrong....
 
Whats an ASD relay?
 
adam_q said:
ASD = Automatic ShutDown
PCM = Powertrain Control Module (i.e. the ECU)
Click to expand...

I know what a PCM is... and if im not mistaken, a 96 xj still has a TCU, which means it has an ECU, not PCM. If the TCM and an ECU are together as one, then its a PCM. Knowledge dropped. Btw, did you change out the relay for it? And what makes you think its bad? If you have no spark, I would check your CKP. Notorious for going bad and not throwing codes. I had a 96 and it would only throw codes when the 02 sensor was bad
 
It's a good question about the year - see my other post with the picture of the PDC which looks nothing like either the '95 or '97 Service Manuals I have picked up from another site.

I'll take a pic of the ECU/PCM to help identify it. Presumably the other unit you are referring to is a Timing module of some sort?

I know the relay is good because:

a) I have substituted a known good one
b) when I ground the Blue/Yellow wire it does pull over, and I get good coil volts on the primary. This is what the PCM is supposed to do (i.e. ground that wire), but isn't.

Point taken about not throwing codes so I suppose I'll start working through the long list checking all the inputs to the PCM.
 
OK so the plot thickens. All sensors checked from the ECU/PCM plugs look OK, e.g. TPS varies linearly, MAP sensor wiring is OK (MAP sensor operation not confirmed yet), temp sensors look like arounf 10k ohms (cold), Park/Neutral switch working, all injectors read around 16 ohms, field coil around 26 ohms.

No problems detected so I reckon it must be the PCM.

Here's what it looks like:

IMG_20110929_182430.jpg


IMG_20110929_182448.jpg


I suppose the PCM/ECU looks like being the next bet, I have a scrapyard nearby which specialises in Jeeps so I may try a replacement, I suppose it's not essential to progam the VIN when changing it?

Also worth noting on the UK spec there is no up or downstream oxygen sensor (the pins were O/C at the PCM multiplug so I then looked at the exhaust - no sensors) so I guess the PCM is programmed differently and ignores them.
 
AFAIK, the forum search function requires at least four characters. Just a quick example: "asd relay" and "asd*" will get some results. See the sticky relating to searches which I assume has something about the four characters.
 
Adam, have you checked the ignition coil?
A faulty coil won't set a trouble code on a 96,
and could be a possibility causing the no-start.

You can also read OBD II codes on a 96. Maybe a
code reader would be able to pinpoint the trouble...?
 
Thanks for the suggestions - the ASD relay provides the coil primary 12V, so if it isn't pulling over to start with then all bets are off regarding the ignition.

What fault codes can you read with the reader that don't show up with the "ingnition on-off-on-off-on-off-on" method? I'll give it a go if it's worth a shot but it means paying my local garage to read them.

Thanks for the ssearch tips - I had already used the google method that accepts 3 characters but will try this too.
 
Searches are coming up with "ASDR" too so that was a good call.

I have one question: when should the ASD pull over on a healthy car?

1. Ignition on not cranking
2. Cranking
3. Running
 
According to the 95 fsm I have, The ASD relay trigger from the PCM also triggers the fuel pump relay. So all 3 should result in an energized relay.

Can you hear the fuel pump prime when turn the ignition on?

The ASD provides power for the Injectors, The Alternator field coil and a pin in the PCM connector along with the distributor and Ignition coil. You should check for power at one/all of those points. I can't tell you which pin in the PCM connector, as the 95 has a single large connector and the 96 has 3 smaller ones.

Power for the ASD is fed through fuse 14 and hits 22 of the relay, it outputs to 24. Power to trigger the relay coil is provided by the ignition. 21 is the positive feed for the coil, 25 is the negative.

I'm sorry if any of this is rambled or something you've tried. I'm just tossing ideas out. I also don't know if there are any differences in the ASD setup between 95 and 96.
 
OK so I was just checking I wasn't trying to fix something that didn't need fixing. If the ASD relay should pull over on "Ignition ON" and it isn't on mine, that's the first thing to fix.

If you scroll up this post to the photo's you can see the PCM has 3 plugs so that's '96 onwards.

After I have verified that the correct ignition-on signal is reaching the PCM (I have checked everything else) then it seems that the PCM itself is the most likely so a replacement is worth looking into.

From what I have seen so far they are interchangeable between cars - can anyone confirm?
 
In post #6, jakbob asks about the CKP (crankshaft position sensor also referred to as the CPS). You later guessed that "the other unit was some sort of Timing module" but I never saw a reply.

Question is: did you ever check the CPS/CKP? This is really the first thing to suspect when these beauties won't start with symptoms such as yours unless you are absolutely sure you know that the problem lies elsewhere. Forgive me if you have done this and I missed the post. Of course you should get a code if the CPS is faulty but it simply doesn't always happen.

BTW, here parts houses will scan codes for free. I assume you know what happens in your own country (been there several times) but thought I would mention it.

Good luck! Let us know about the CPS.
 
Thanks for the pointer. I had intended looking at the CPS at some stage, but up till now I hadn't considered it because the sequence of events is:

1) turn on ignition
2) note that ASD hasn't pulled over
3) turn ignition one click to start - we are now cranking

Now the CPS will only come into play when I start cranking, will it not? I.e. you either get pulses or you don't. The PCM won't care about the CPS until stage (3), but at stage (2) I still have the ASD fault, so therefore no spark or injector power.

I have a good few hours to investigate today so I'll start looking at more stuff feeding the PCM including the CPS. I have also given it a good charge up so lest see if that makes a difference.

Incidentally did you look at the pictures - can you confirm that this is a PCM? Cheers.
 
Next update - all inputs check out OK, including the CPS. Nominal or varying voltages on everything as expected, and measured at the 3 multiplugs.

The CPS outputs 0.01V with ignition on, and during cranking around 0.17V. This would means around a mark/space ratio of around 3% and 5V pulses. I think this sort of makes sense - I didn't get the 'scope out to check the pulse shape though.

Looks like I am looking for a new PCM then... anyone changed them over - anything to watch out for?
 
.. and what exactly am I looking for, a P56041 297, or are there any other numbers to look for?

One further update - I started investigating pulling the relay over by grounding the PCM control and noticed that the PCM does in fact pull over the ASD for about 1 second just when you switch on the ignition, but it doesn't hold.

I think there's a latch-up circuit in the PCM which is supposed to hold the relay, and this isn't working. The ASD output definitely reaches the PCM though, which I think is the signal it would use to hold the relay closed, so it looks like the PCM is deciding not to hold it for reasons of its own.

Notice this is all _before_ going the further click on the ignition switch to start cranking.


 
Last edited:
What fault codes can you read with the reader that don't show up with the "ingnition on-off-on-off-on-off-on" method? I'll give it a go if it's worth a shot but it means paying my local garage to read them.
Click to expand...
A code reader will give the 3-digit OBD II codes, which are more
precise than the 2-digit OBD I codes. The 1996 model year was a
transition year in which both OBDs were used by Jeep. If you have an
OBD II port located under the dash to the left of the steering
wheel, then it'll give OBD II codes. This may or may not be of any
help though, since you presently don't get an OBD I trouble code....

Are you sure the ASD relay itself is good...?

Sounds like the CPS is OK, what about the cam position sensor
located inside the distributor? Those two sensors are the main
causes of no-start situations, and I've had a cam sensor failure
on my 96. (It did set a fault code, however.)

This is a mystery to me; just trying to throw out some ideas...
 
Yes the Cam position sensor is fine, I see +5V,0+5V,0, alternating on cranking.

A bit later on I will post up all the readings I made from all the inputs in case that flags up something to someone.

I of course substituted the ASD relay for known good ones (there are 4 others to choose from in the PCD as you can see from the photo) and of course it works fine if you ground the ASD control wire manually.

Under the manual grounding test the thing still won't start but I suppose the ignition pulses and injector pulses are under the control of the PCM so it needs to play ball. It might be worth trying this again and see what I do and don't get.

Incidentally Jeeps of this vintage are now only worth around £300 here in the UK so I ain't gonna be throwing lots of money at it! I shall definitely shop around if I need a new PCM.
 
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