DTC P1371 IC 4X Reference Circuit Too Few Pulses
DTC P1641 Malfunction Indicator Lamp (MIL) Control Circuit
DTC P1642 Vehicle Speed Output Circuit
DTC P0300 Engine Misfire Detected

I think the last one may not be clearing since the first 3 are "Manufacturer specfic codes" but thought I would post them all. What could this be? A control unit of some type? Thanks guys

 

Are these for your Z, or another vehicle?

 

The P1371 and P0300 are related (especially P1371) to the opti-spark distributor taking a dump. The P0300 is probably setting due to the reason for the P1371.
P1641 sets if the circuit to the instrument cluster to indicate a DTC is shorted/broken.
I'm not sure about P1642...haven't found that one yet, but could be the VSS in the trans is bad.
Am I sure ?
I'm an electrical engineer within the GM headquarters....you be the judge.

 

Alright well i just replaced the opti b/c i was told it was bad, the codes havent cleared and they tried clearin the codes and said they couldnt because they were manuf specific. so wtf do i do? I doubt this opti is bad as it would be acting up in some sorta way if it was and it drives fine, pulls hard and everything. could it be something with ICM?

also with "P1641 sets if the circuit to the instrument cluster to indicate a DTC is shorted/broken."

what do i do to fix that is it a short or like something else that is easily replaceable or does it have to really be torn apart to find out?

let me know if you find out about "I'm not sure about P1642...haven't found that one yet, but could be the VSS in the trans is bad."
is that accessible or have to tear tranny appart? sorry for so many questions just want everything fixed thanks for all your help man

yes for the z

 

According to my OBDII manual, with GM tech info, the code definitions are not for a V8 F-body. They are for a different GM vehicle.

The manual says the code definitions are:

P1371 - DI ignition low resolution circuit
P1641 - Fan control relay 1 control circuit
P1642 - Fan control relay 2 and 3 control circuit
P0300 - Random misfire

As the previous poster says, the 1371 and 0300 are related. You changed the opti with no change in symptoms, so it's time to check wiring and plugs. A scan tool with enhanced capabilities can help pinpoint the random misfire.

 

well i was havin a problem with the car dying and missfiring b4 i changed the opti now it doesnt do it. just for clerification also not sure if i stated but i did the wires when i changed the opti and the plugs were just done like a month or two ago... might end up taking her in if i cant get an idea where to go, i could check the plugs even though the PITA job it is lol but the funny thing is it never randomly missfires like the code suggusts, been drivin it for the last 3-4 days. I could check the plugs. what else? (sry have yet to goto bed after work i work nights lol)

 

Have you had anyone clear the codes ?
These codes may only be in history, not current codes; clear them (battery disconnect in most cases will NOT clear OBDII codes) and see if they return.
For the fan DTC, check your fan fuse.
How new is the ignition coil and the ignition module mounted to the coil ?
These could cause mysterious misfire codes, but not the Opti resolution code.

 

Some OBD-II codes will clear with the power disconnect, others will not. Try pulling the "PCM BAT" fuse (key in "off" position") for 30 seconds and see what happens.

For LT1 codes, always check Shoebox's online LT1 code lists (OBD-I and OBD-II) to get LT1-specific code descriptions, and not the "generic" ones that show up on scanners or on other lists. That would have avoided your initial error on the descrptions, and the continuing error on the first two replies posted above.

http://shbox.com/1/Dtcs.htm

 

Thanks Injuneer

also they could not clear the codes, they said that because they were "manufacturer specific" it would not allow it (well at least at autozone/checkers ect)

I'll try pullin it and let ya know what happens