No Codes when powered up off board
Thread Starter
Staging Lane
Joined: Jul 2018
Posts: 76
Likes: 4
No Codes when powered up off board I've got the original PCM/harness from my 2003 Express Van 6.0L donor vehicle. I wanted to retrieve the VIN from the PCM to be sure of what I had. I wired a DLC and powered it up. I was able to view the data I needed with a Snap-on scanner, however I noticed that the PCM didn't set a single trouble code. I thought this was pretty curious. Not a single thing was plugged into the PCM other than the scanner. As an experienced mechanic, I was expecting a trouble code for just about every sensor it was expecting to see. No U codes for the other missing computers....nothing.
In my years of working on cars I've never tried this before, so it may be normal, but it was certainly a surprise to me.
Anyone else ever notice this?
Joe
In my years of working on cars I've never tried this before, so it may be normal, but it was certainly a surprise to me.
Anyone else ever notice this?
Joe
TECH Fanatic
Joined: Dec 2017
Posts: 1,467
Likes: 265
From: Bossier City, Louisiana
It is normal. Without any constant 12 volt "keep alive" memory power to the PCM, the box will have a complete amnesia loss of any DTC codes, shift adapts or other learned throttle parameters. All you will see is what is burned into non-volatile memory such as the VIN and the semi-hard coded tune parameters.
This is why the engine is often a little difficult to start when the 12 volt battery has been removed for more than a few seconds. But crank the engine up and give it 30 seconds and you should be good to go again.
Rick
This is why the engine is often a little difficult to start when the 12 volt battery has been removed for more than a few seconds. But crank the engine up and give it 30 seconds and you should be good to go again.
Rick
Thread Starter
Staging Lane
Joined: Jul 2018
Posts: 76
Likes: 4
Thanks Rick! Glad it's normal. I figured any history codes might be missing in action, but I was puzzled why it didn't set any current codes. Coolant Temp, IAT, MAF, Crank, Cam, Injectors....everything is unplugged. The PCM normally doesn't have to see a running engine to set open circuit codes, or Data Bus codes. I guess if it sees nothing is plugged in it doesn't complain about it. Either way, I'm glad I'm not the only one that has noticed it.
Joe
Joe
