Code for ECU came up on diagnostics

FRANK W. HUNT

MEMBER
1999 JEEP GRAND CHEROKEE LAREDO
4.0L
6 CYL
2WD
AUTOMATIC
238,671 MILES

I took my vehicle to Firestone Auto Care and had them plug their OBD reader into it and a bunch of codes popped up that do not pop up on the on board diagnostics. How do I fix a diagnostic issue? Also one of the codes that popped up was a malfunctioning ECU. Will that cause other types of diagnostic codes if it's just an ECU problem? I can't find any references to any troubleshooting in my Haynes repair manual.

1 Reply

STEVE W.

MECHANIC
13,465 POSTS

It depends on what the actual code is. There are multiple codes that can mean anything from the ECU needs to be updated to the ECU has to be replaced. As for the codes showing up on their machine but not the onboard, that is common, the onboard doesn't show all of the possible codes the vehicle can have. However the better option would be to have a different place scan the vehicle, then post all of the codes they show, along with any the onboard display shows and we can proceed from there, there are many different troubleshooting options but to get on target the codes are needed.
Is the check engine light on now? If so what codes does the onboard show?
Any issues driving it?