Code reading - When is a code considered History?
Thread Starter
Team Owner
Joined: May 1999
Posts: 22,830
Likes: 13
From: Columbus Ohio
CI 3-4, 8-9-10 Veteran
St. Jude Donor '06-'08-'10
Code reading - When is a code considered History?
Tried searching but had no luck funding anything that defines when "C"urrent rolls over to "H"istory. 
I had the check engine light come on this morning so I pulled the codes when I got home.
The only "C" codes were for "TPM Sensor Malfunction." Fooled GM on that one. They're not malfunctioning, they are gone completely.
The only code I see that might trigger check engine was P0300H for engine misfire. The check engine light was still on coming home so I'd think it would show as "C"urrent. Any thoughts?
And if your hand writing sucks like mine you can download the Excel spreadsheet below and just enter an H, C or both in the left column to record any codes.
Excel Code Check List
I had the check engine light come on this morning so I pulled the codes when I got home.
The only "C" codes were for "TPM Sensor Malfunction." Fooled GM on that one. They're not malfunctioning, they are gone completely.
The only code I see that might trigger check engine was P0300H for engine misfire. The check engine light was still on coming home so I'd think it would show as "C"urrent. Any thoughts?
And if your hand writing sucks like mine you can download the Excel spreadsheet below and just enter an H, C or both in the left column to record any codes.
Excel Code Check List
Last edited by Blue 92; Jul 16, 2008 at 08:28 PM.
Intermediate
Joined: Mar 2008
Posts: 28
Likes: 0
From: Denton Texas
The only time a code becomes History is when it's no longer being triggered. I'm pretty sure some History codes will leave the Check Engine Light on. If you've got the codes recorded somewhere, like that excel sheet, just clear the codes and see if the light comes back on. If it does and there are codes that are only shown as history you can bet that's what's causing your problem. You just aren't checking the codes when they are being triggered. And then again I could be wrong, some guru might come along here and make me look like an idiot 
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
Different codes have different "rules" ....
Most OBD2 mandated codes will set to an H satus once the test that set the DTC is passed ... but if the MIL was turned on by that code the MIL will often stay on until the test has passed 3 consecutive times.
EBCM codes ALWAYS set to H status when you turn the ignition off. When you start the engine the EBCM runs its diagnostics and sets any codes if something is failing. During that ignition cycle the codes set will show "C" but will go to "H" at engine shutdown.
Some codes can even show a dual status .... they can have both an H and a C after them .....
Bottom line, don't read too much into the status unless you know the rules for the status of that code .... treat every code as if it were a current code.
Most OBD2 mandated codes will set to an H satus once the test that set the DTC is passed ... but if the MIL was turned on by that code the MIL will often stay on until the test has passed 3 consecutive times.
EBCM codes ALWAYS set to H status when you turn the ignition off. When you start the engine the EBCM runs its diagnostics and sets any codes if something is failing. During that ignition cycle the codes set will show "C" but will go to "H" at engine shutdown.
Some codes can even show a dual status .... they can have both an H and a C after them .....
Bottom line, don't read too much into the status unless you know the rules for the status of that code .... treat every code as if it were a current code.
Thread Starter
Team Owner
Joined: May 1999
Posts: 22,830
Likes: 13
From: Columbus Ohio
CI 3-4, 8-9-10 Veteran
St. Jude Donor '06-'08-'10
Different codes have different "rules" ....
Most OBD2 mandated codes will set to an H satus once the test that set the DTC is passed ... but if the MIL was turned on by that code the MIL will often stay on until the test has passed 3 consecutive times.
EBCM codes ALWAYS set to H status when you turn the ignition off. When you start the engine the EBCM runs its diagnostics and sets any codes if something is failing. During that ignition cycle the codes set will show "C" but will go to "H" at engine shutdown.
Some codes can even show a dual status .... they can have both an H and a C after them .....
Bottom line, don't read too much into the status unless you know the rules for the status of that code .... treat every code as if it were a current code.
Most OBD2 mandated codes will set to an H satus once the test that set the DTC is passed ... but if the MIL was turned on by that code the MIL will often stay on until the test has passed 3 consecutive times.
EBCM codes ALWAYS set to H status when you turn the ignition off. When you start the engine the EBCM runs its diagnostics and sets any codes if something is failing. During that ignition cycle the codes set will show "C" but will go to "H" at engine shutdown.
Some codes can even show a dual status .... they can have both an H and a C after them .....
Bottom line, don't read too much into the status unless you know the rules for the status of that code .... treat every code as if it were a current code.
I did see that TPS sensors were showing both H & C.
Had a total of 12 codes. 4 were the TPS, 7 related to when I drained the battery while installing the shifter (door and interior lights on too long).
That left me with only the "P0300 Engine Misfire Detected" as the possible cause for the check engine light. I'll see what happens next time I drive it.
