AccordSwagon

Recently I bought a 2000 Cherokee Sport 4.0L Automatic.
First jeep, excited to get it reged/inspected and on the road, and build it up.
Had two codes, trans and p1388. Didn't think the relay code would be an issue, didn't know what it was. Fixed the trans and kept driving it around to clear the 4 readiness monitors.
Noticed none of them are clearing, and was weird.
(Guy I sold it from had a temp inspection sticker on it, so I assume he wasn't able to clear them down to two readiness monitors for NYS inspection for passing)

So I opened the fuse box to check the relay and I see that the ASD relay is jumped. Remove the jumper or put a relay in it and then jeep will just crank, won't start.

Trying to diagnose the harness, kinda a little lost with electrical diagnosing, couldn't find anything wrong.

Today we took my ECU out and put it into a friend's 2000 xj, would crank but won't start, if we do the jumper on his jeep also, works then.

So then we took his ECU and put it on mine, also put in a relay into the spot instead of the jumper. When you out it into ignition, the ASD relay makes a buzzing noise. But if you turn it to crank, the vehicle will crank and run. Once it's running, the relay doesn't make any buzzing noise.

So I assume the ECU is bad, will order another programmed one.
(Checked all the fuses and they are good too)
(also checked pin 3 on the gray plug to the relay socket and it has continuity)
But there still is the issue of why is that relay buzzing, know it's not suppose to.

Can anyone suggest where/what to start checking?

Have seen other threads/forums online but just seems it could be pretty much anything so I'm a little lost on how to narrow it down.

Thanks!!!

Oldsrip

The ecu supplies power that pulls the relay closed so it supplies power to the injectors, etc.

If the ecu isn’t suppling the power, you can rewire the circuit around the ecu. You have to find a way to have power go to the proper terminal of the relay with the engine in crank and run position.

Or do it right and replace the ecu.

I don’t have a schematic for your year. But recently had a issue with a 96 xj. I am guessing that your is wired similar.

AccordSwagon

Wired like a Chrysler lol. Believe the previous owner changed the motor and messed something up.

think I'll have to wire it proper so no codes will pop up and I can clear the readiness monitor for inspection.

Just have a hard time with tracing wiring issues

BlueRidgeMark

No, this is not correct. The PCM supplies GROUND to trigger the injectors, not power. Same for the coil and other things operated by the PCM.

Do NOT wire around it!

This tells me there is something wrong with the wiring to your vehicle's ASD relay. Ignore that, and put in a new PCM, and you are likely going to fry it again.

If a new PCM goes in, and you have wired around it, you'll regret it. Maybe not today, and maybe not tomorrow, but soon, and for the rest of your life.

AccordSwagon

I gotcha haha. Know it supplies ground to pin 3 on the gray connector, which if I can remember is a blue wire with yellow stripe.
I checked the continuity between the relay socket and ECU plug and checks out fine.

Just a little lost on what to check next. (What's causing the relay to buzz)


(not mine, what it feels like)

Oldsrip

[QUOTE=BlueRidgeMark;3657929]No, this is not correct. The PCM supplies GROUND to trigger the injectors, not power. Same for the coil and other things operated by the PCM.

Do NOT wire around it!



Hi Mark,

that’s what I was thinking too.
here is what we found. Tell me if I am misinterpreting something.

we pulled the grey plug from the ecu. There is a green wire with yellow tracer that runs to the asd relay. We put 12 v to that wire and it powered up the circuit.
I was testing power to the o2 sensors. So I had the dvom hooked into the o2 sensor plug.
as soon as we hit that wire with power we had our 12 volts to the o2’s.

If t required a ground to power that side of the relay, putting power to it shouldn’t have worked?

if I'm wrong I want to know. Always learning

funny thing is, we were testing for 12 v to the o2’s with the key on engine off per the instructions found on the internet.
it turns out that the info was wrong. It has to be cranking or running for 12 v to be supplied to that circuit.

BlueRidgeMark

Aha! Turns out I have the FSM for the 2000 model year. Here's what it says about the ASD relay:

DESCRIPTION
The ASD relay is located in the Power Distribution
Center (PDC). The PDC is located in the engine com-
partment. Refer to label on PDC cover for relay loca-
tion.
OPERATION
A 12 volt signal at this input indicates to the PCM
that the ASD has been activated. The relay is used to
connect the oxygen sensor heater element, ignition
coil and fuel injectors to 12 volt + power supply.
This input is used only to sense that the ASD relay
is energized. If the powertrain control module (PCM)
does not see 12 volts at this input when the ASD
should be activated, it will set a diagnostic trouble
code (DTC).


In general, a buzzing relay is caused by low voltage at the coil. The low voltage is almost enough to keep it engaged, but not quite, so it 'chatters', or buzzes. I'd be looking for the supply voltage to the relay, and I'd be looking very carefully at the grounds. See my sig, #1. There's a link there for all of the ground locations, courtesy of one of the forums old-timers.







Pin-out type 2 relay





I need to run for the moment. I'll try to dig up the schematic later today.

AccordSwagon

Ooo, looks like it will help checking it out! Will use it when I get home from work. See what voltage I'm getting and if I see any corroded grounds.

Did notice when the Jeep was running, at the battery I was getting like 16.4v

lawsoncl

It's already "wired around" with that jumper and working, but the ECM isn't happy that it can't control the ASD relay. Best guess is that instead of properly troubleshooting the problem, the PO jumpered it incorrectly and blew the driver transistor in the ECM.

AccordSwagon

Probably had something to do with then they swapped the motor. Either messed up the harness (break/or short) or a bad grounding somewhere.

Does start up with the relay and a "new" ECU. Just that relay buzzes. Going to test grounds later.

The new ECU does come with a one year warranty but don't wanna push it, Want it right.

BlueRidgeMark

That ain't good.

AccordSwagon

Not sure if the over voltage is from the pcm issue or alternator. Looks like the original alternator, so I ordered a new one.

lawsoncl

Poor grounding to the ECM can cause a high voltage. Your alternator is likely fine, as it's the ECM that controls the charging.

BlueRidgeMark

Poor grounding can cause a whole host of weird problems.

Don't just look at them. Take them apart and MAKE them good.

AccordSwagon

I took off the grounds closest to the harness, brass wire wheeled them and the screws and put them back

Will do more later on tomorrow.
Did notice one grounding strap towards the back of the motor/firewall is broken. Don't see where it went to.

Was like a 1/2" braided flat copper ground strap.