I picked up my truck today from the transmission shop and the check engine light was on. They checked the codes and it had the 1688 code. It starts and runs fine as it has since I got it and never has had any symptoms of failure. It did have a light come on about a month ago, but it went off after two days before I had the codes checked. It has never acted as if there as any pump problem.

Is there any chance the batterys being unhooked during the transmission swap or the power puck are causing this? They did clear the code and it did fine tonight driving.

I know everyone says it is a death code, but everyone also seems to have failure symptoms.

BTW, the pump only has 12K miles on it since replacement by the previous owner.

 

Clear the fault code, turn the ignition key OFF for at least 60 seconds, turn the key ON. Without starting or cranking the engine check if P1688 resets. If P1688 resets at key ON, replace the injection pump. If the fault only resets with the ENGINE RUNNING, look for a loose power or ground connection to the injection pump, or a bad fuel pump relay.

 

Well, we reset the code and it did not come back.....can I assume grounding issue?


Thanks!

 

Load test the injection pump power and ground at the injection pump connector using a head light as a load. Light should come on bright if not check relay and ground. Substitute a known good relay and recheck if light comes on bright as if hooked directly to the battery.



FUEL INJECTION PUMP (DIESEL) - 9 WAY CAV CIRCUIT FUNCTION
1 K240 20BK DATA LINK (-) FUEL INJECTION PUMP
2 K242 20WT DATA LINK (+) FUEL INJECTION PUMP
3 - -
4 K44 18VT/OR LOW IDLE SELECT
5 K45 18LB/RD FUEL SHUT-OFF SIGNAL
6 Z12 14BK/TN GROUND
7 A40 14RD/LG FUEL PUMP RELAY OUTPUT
8 K48 18DG FUEL INJECTION PUMP SYNC SIGNAL
9 - -

 

Just to make sure I am 100% clear on the load testing...

I simply unhook the harness, hook up a headlight to the 1 and 2 terminals and turn the key on?

I want to make sure because I have read several times about "load testing the pump", but to me this is load testing the pump power circuit. I assume this is on and the same?

Thanks!!

 

Pin 6 and 7 is power and ground. pin 1 and 2 are data link to ECM.
Load the circuit with headlight pin 6 and 7 only.