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P1643 with new KOJO tune

bfourman

bfourman

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Location
Vincennes, IN
I installed my new Walking J/KOJO tuned ECM this afternoon, and the truck performance is outstanding! I am having an issue with DTCs though. I did the KOKO procedure as advised by Patrick, no problems there. I am getting a P1643 code, which on my scanner is a Fuel Pump Control Circuit fault. Once I clear it it doesn't come back on on restart as long as I have the scanner plugged in. As soon as I unplug the scanner and start it, the SES comes back on. The WTS light comes on, the glow plugs cycle and the lift pump purrs away, but the light comes back. I never had a light with the stock ECM.

Any ideas? I don't have access to a TechII or anything past a OBDII scanner so I can't give info on timing or otherwise.

Truck and mod info in my signature.
 
Hi,

I have gm books only for 1995 (obd1) and 1999 and that 1999 book says code P1643 is Wait to start lamp control circuit fault. You said wts light comes on, so feels little weird, homever, i did found this from google : " i'm still getting the P1643 after a couple starts but Bill said could be a bad ground somewhere or even a burnt out bulb in the instrument cluster not related to the glow plugs at all, i'll have to take some more time and check it out. but the timing is properly set and that was the most important."
One thing what i want to add that thing is: is there right type bulb in wts light? i think it is possible that lamp isn't taking enough current and thats why computer thinks it isn't working. (DO NOT short circuit bulb circuit)
 
Actually, the PCM doesnt control the WTS light on this vehicle. The PCM only monitors that there is voltage to the WTS light. I dont know if P1643 is even a valid code for a 1996 truck though. I attached the schematic available for 1996 truck.

This DTC does not appear in the tech data for the 1996 truck on AllData: P1643 Wait To Start Lamp Control Circuit
AllData has been missing info in the past though.

The PCM in this case does not control the WTS lamp, by grounding it and pulling current through the PCM. I dont know if it is different in 97+ trucks. The PCM here as is with my OBD1 truck is merely looking for voltage on the line.

There are a couple possibilities. The Program is meant for a later model truck. Or the D7 PCM input wire got broken in the process of putting the new one in. So if you put the old PCM back in and it goes away then I would guess the PCM program file needs to be specfic to the 1996 year. If the "Glow Plug" fuse was blown you may get this DTC, but then you wouldnt get the WTS light either. If the manual for a 1999 has the PCM as the ground for the WTS light then it would make more sense that this DTC would apply to a later model truck. It could also be a failing glow plug controller. Because the PCM program may have extended the glow times, sending the signal to the controller, but the controller may have cut power to the GPs prematurely, which would be seen by the PCM and suspect the WTS circuit is bad.
 

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  • 1996_GP_circuit.jpg
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My scanner is the "enhanced" version of an OBDII scanner in the fact that it displays the code description along with the code. I can select the year, make, model, engine and trans combo when I read the codes, maybe in 96 it was a different code than 97+.

Code goes away with the stock computer. The glow plug controller clicks in sync with the WTS light.
 
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make sure all your connections by the computer are nice and tight. there was a thread a few days ago that had a loose connection after swapping ecms and it was causing stalling and misfires. its a shot in the dark but its a possibilty
 
I would not trust what the scanner has, they never get the code descriptions right for this truck, because GM used some of the same numbers for other vehicles meaning differnt things. So unless you have a manual that says what the DTC really is hard to tell if its right. I have a few of those scanner books and none of them are right for my year truck compared to the actual GM diesel supplement manual.
 
I'll check the GP wiring this week at work, if everything checks ok I guess I'll have to live with the light or pull the bulb.
 
bfourman said:
The glow plug controller clicks in sync with the WTS light.
Click to expand...

Yes, let us know what you find out.

I wanted to comment that the WTS light will always work in sync with the controller clicking on and off. What I meant by a possible failing controller is that the PCM may be commanding 15 seconds of glow time, but the controller may click off after 9 seconds, and the WTS light woud lose voltage and the PCM would see this loss in voltage to the PCM. And it could code because it clicked off 6 seconds short of the time it had been sending the glow signal to the controller. Thats not necessarily what is happening in your case, just a thought. because stock PCM may have only been calling for 9 seconds of glow, so it wouldnt code, but the Kojo tune increased it.
 
Good point Buddy! if bfourman doesn't find any problem wiht glow system i try to find truck close as possible of his and test that software in it, it will tell if problem is in ECM or software, we will work this out, but it takes just some time.
 
To update this, Kojo sent me a whole new ECM with an new tune. The SES light is gone, truck still runs great!

Thanks again to Kojo and Walking J!
 
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