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Check Engine Light on/off after new battery installation

PostPosted: Fri Oct 16, 2020 10:49 am
by Barrykl
I've had a CEL on for two months, then my battery finally died. I installed a 26F replacement and the CEL went off immediately.

72 hours later, the CEL came back on and was on all day yesterday driving around for about 2 hours in one direction and two hours in another.

I'm just looking for some ideas, is this likely an electronics issue because of the CEL timing?


extra info I don't know the significance of:

My ABS light also comes on sporadically, usually for 30 minutes or so, then turns back off while driving around, specifically after fixing the shifter cable last week.

Re: Check Engine Light on/off after new battery installation

PostPosted: Fri Oct 16, 2020 12:56 pm
by catbrown357
Always post year and model if you want help diagnosing problems.

2004 Isuzu Rodeo CEL troubleshooting

PostPosted: Fri Oct 16, 2020 4:53 pm
by Barrykl
Sorry about that - 2004 Isuzu Rodeo with these CEL issues

Re: Check Engine Light on/off after new battery installation

PostPosted: Fri Oct 16, 2020 5:08 pm
by Tentin
Well, it sounds like you need to scan your check engine light and take care of it. Replacing/disconnecting the battery will reset any codes you had stored which explains why it went away temporarily.

Lots of parts stores will scan OBDII codes for free, otherwise you can get a $10 bluetooth adapter that hooks up to your phone and you can scan them yourself using an app.

As for the ABS light I'd first make sure your brake fluid is topped off.

Re: Check Engine Light on/off after new battery installation

PostPosted: Fri Oct 16, 2020 6:35 pm
by Barrykl
Great, I have an obd2 reader, I didn't know all the codes were reset upon battery replacement. That's good to know! Thanks for your help, I'll start troubleshooting.

I was thinking it would have to be an electrical thing because of the battery, but if the codes are reset I'll get back to the codes. Thanks again.

Re: Check Engine Light on/off after new battery installation

PostPosted: Sat Oct 17, 2020 12:54 pm
by Buster28
If you clear a Diagnostic Trouble Code (DTC) using a scan tool or by disconnecting the battery all the Readiness Monitors will reset to a Not Ready state and it will take several drive cycles before they will be set Ready. These are the Readiness Monitors implemented in your Rodeo:
Misfire (continuous)
Fuel Trim (continuous)
Comprehensive Components (continuous)
Catalyst (CAT)
Exhaust Gas Recirculation (EGR)
Evaporative (EVAP)
Oxygen (O2) Sensor
When the Readiness Monitors are Not Ready some diagnostic tests are not run. Once the monitor is set Ready the CEL will illuminate with the same DTC set if the malfunction was not repaired. The Readiness Monitors prevents cheating a state emissions test. You can turn off the CEL but you can't set a Readiness Monitor to Ready and the vehicle cannot pass the EPA emission test with one or more monitors Not Ready.

The ABS Warning Lamp will automatically reset after the fault has been cleared and vehicle speed is greater than 11 mph (more or less). The ABS Warning Lamp cannot be turned Off by removing the battery or using a scan tool. Even removing the ABS module electrical connector will not turn Off the ABS Warning Lamp. Be aware that some inexpensive scan tools/readers cannot communicate with the Isuzu ABS electronic module using the 16 Pin Data Link Connector (DLC) digital serial data buss.

Btw, low brake fluid will illuminate the Brake Warning Lamp but not the ABS Warning Lamp.