Cobra ECU PCM Test Procedure?

[lucheski]

How can I test that ECU/PCM is receiving power and ground? What is the test procedure to make sure the ECU is coming online and functioning properly?

 

[hotcobra03]

start car. if it runs it’s worling

 

[lucheski]

This is what I found so far..Maybe this will help someone who searches in the future

 

[SVT Hess]

What symptoms are you having that make you question your ecm? I recently went through majority of those tests trying to figure out a issue with my car.

 

[lucheski]

What symptoms are you having that make you question your ecm? I recently went through majority of those tests trying to figure out a issue with my car.

Crank no start, no prime to fuel pumps. THe PCM/ECU is completely unresponsive. A locksmith came over and attempted to cut me a new key his tool displayed "No ECU found". SCT Handheld also displays codes "No vehicle attached to device " "ECM Unlock Fails" Bob Kurgan said if it was a only PATS issue the fuel pumps would still prime and it could be the PCM not sending signal to CCRM to prime the pumps. I set the cluster in self-diagnostic mode and pulled codes from instrument cluster and got code that said "Non-Volatile Memory (NVM) configuration failure - No PCM ID stored in PATS."


Already checked EVERYTHING else.
Fuses,
Relays,
Inertia switch,
Pumps jump manually,
Took apart CCRM tested relays inside individually. Even tried a new CCRM just to be certain.

[bcolor=rgb(255, 255, 255)][/bcolor]

 

[lucheski]

So I am doing this last test of the PCM itself before trying to replace it

 

[hotcobra03]

1st. was any work done before having issues?

like or parked car and next time nothing?

 

[hotcobra03]

i had the ground wire on radiator support crack on the eye. at a red light. went to go on green and car died in middle of road. same problems as this.

dashes in odometer
no crank
no scan

 

[SVT Hess]

Definitely a different issue than what I had, my issue was I would lose majority of my power and would find the voltage on the ground side of the circuits. Long story short, it was the starter. I never had no ecm detected but when I would plug my SCT handheld in I would get power back to the car, annoying issue to track down as I picked up a spare ecm abs module and few other things because it always seemed to lead back to something in that circuit that was my issue but alas it wasn’t.

 

[lucheski]

Where is the PCM Power Relay and Fuse located?

I pulled the connector off the PCM last night and I am not getting KeyON/KeyRun Power. I get power on the Always on power wire and tested all the grounds.

 

[hotcobra03]

f1-26 pcm fuse
pcm relay is in ccrm

 

[lucheski]

It was the fuse F1.26 (engine compartment); 40A large size fuse; powers the PCM and CCRM.

I put a new one in and started the car, then blew the new fuse. Do you know what makes the fuse blow repeatedly?

 

[MG0h3]

It was the fuse F1.26 (engine compartment); 40A large size fuse; powers the PCM and CCRM.

I put a new one in and started the car, then blew the new fuse. Do you know what makes the fuse blow repeatedly?

short circuit; usually to ground. Example would be a chafed wire.

Other possibility is somehow you are drawing too many amps.

Grab a wiring diagram if you haven't. One side of that fuse has power from somewhere, the other side feeds power to the pcm and ??


Edit: so you actually got the car to start or it popped as soon as you went to crank?


Sent from my SM-G950U using the svtperformance.com mobile app

 

[BlckBox04]

start car. if it runs it’s working

lol

 

[hotcobra03]

you have a short.

fuse 2 and 8. inside car

engine controls

the big engine harness connector with 10 mm bolt.

unplug connector

install new fuse in f26

turn key and see if fuse blows again.



what you are doing is isolating the short.

most of the time it’s on engine a component is shorting.

there was a thread about a month ago in tech section about pcm fuse blowing.

 

[lucheski]

It's a E85 car so typically it starts runs rough then dies when cold till it gets some heat in the motor, then you just start it again. Fuse blew after running for several seconds. I am going to try procedure below as I search for the problem. I had just changed the spark plugs so I will check the ignition harness first for any shorts

To save your money on fuses, you don't need to use one for your testing. At the fuse box, with the fuse out, find out which side is the 12v side. The "other side" is the "circuit" side. From here / there, you can attach your meter and MEASURE resistance to a KNOWN GROUND. IF you are "lucky", with your key in "OFF", the readings should be high / very high / to open circuit. When you turn your key to "ON" (not start), you should see some resistance level... lower than before BUT not ZERO.... when it goes to ZERO that is when you are doing the "fuse blow" thing. Once you observe these "activities", you may be able to start further down the road to isolating your problem. Let me / us know if your observations concur with the description provided. Actually, I suspect that you might not see a "ZERO" at all because since there is no current running (ie. fuse is missing), that your "soft fault" might be relay related (ie. weak / worn winding) which may only show with juice applied

 

[lucheski]

you have a short.

fuse 2 and 8. inside car

engine controls

the big engine harness connector with 10 mm bolt.

unplug connector

install new fuse in f26

turn key and see if fuse blows again.



what you are doing is isolating the short.

most of the time it’s on engine a component is shorting.

there was a thread about a month ago in tech section about pcm fuse blowing.

I get the concept of isolating the short. But what does it tell me if the fuse blows (or not) again with the PCM disconnected?

 

[hotcobra03]

I get the concept of isolating the short. But what does it tell me if the fuse blows (or not) again with the PCM disconnected?

just to confirm now.

with f26 in.

you can turn key to on position and scanner should read pcm over circuits 914/915.

but once you turn key to run f26 pops

 

[lucheski]

I disconnected the PCM, still have short to ground.
0 ohms of resistance testing from the power (left) side of F26 Fuse to the engine block.

I am going to test the short using the PCM connector itself so I know which circuit has the short to ground, should save time, I will update

I also tested 5 of the 8 the COPS harness connectors for shorts I am showing 10 - 11 Mega ohm resistance between positive and negative at the COP connectors is that normal? I don't think that's my short since 10 Mega ohm resistance is pretty high and fuse block is showing 0 ohms resistance. Key was off

 

[SVT Hess]

This may be a long shot but since you said you just did plugs,on the back of both heads is a single red power wire that goes to the noise filters according to my wire diagrams. Those red wires are hot on key on, as they get power from fuse 1.26, it’s possible one may have gotten pinched. Follow your coil harness and you will see the single wire I’m talking about. hotcobra03 has a good point, if you disconnect the big harness connector in your driver side fender well that will isolate fuse 2.8 and 2.2 from being possible culprits. If the big fuse blows with that part of the harness disconnected then it’s not on the 2.8 or 2.2 circuits most likely.