Engine/Transmission (1998.5 - 2002) check engine light

[RHoch]

code reads no communication from ECM to injection pump. any ideas what this might be? rpm are high when first started then the light comes on. this only happens once and a wile. the trucks a 99 2500 4x4 with edge comp box and fass pump.

 

[Andy Redmond]

What's the code #, 1688, 1689 etc. ?



Look at my "From the Shop floor article" in the most recent issue.



Since your issue is intermittant it might be more challenging.



Get the pin out for the ECM connector from the FSM. Monitor the power, grounds, bus circuits etc. to the fuel injection pump connector.



You can also ck. the harness (focus on injection pump to ECM) pins by ohm'ing out and ck. for short to ground on each pin.



Also carefully ck. the engine harness near the ds shock tower for Cummins bus wire/fuel injection pump relay (ECM to relay) trigger wire chaffing causing a short to ground.



Be really careful with these fragile connector pins. Use a sewing needle etc. vs jamming your multimeter pins into the connector. If they get stretched or cracked you will really have some fun on your hands.



Good luck

Andy

 

[Andy Redmond]

Opps. . disconnect the Edge box. See if gremilin returns. Sometimes when a tuner fails it messes with the apps and or ECM/FIPM (fuel inj. pump module) and causes it to "high idle" by itself.



Also you will notice by looking at the APPS connector that it has two idle validation "switches" a ref. voltage, two grounds and signal out voltage circuit.

 

[ghass]

Not sure this helps you, but for my '99 3500 model Dodge, more than once I have had my check engine light go on after first starting vehicle, then extinguish. I believe it was due to low battery voltage before/during the start, say around 10-11 volts on the instrument panel I would guess. I have a 5th wheel RV which when that battery is low, can suck power from the truck as there is no isolator in the circuit. Hence, a false interpretation of a signal.

Watch your meter in the truck dash to see it shows the voltage low before you hit the starter. That may be a clue. I'm definately NOT an expert: consider the source of this information in your analysis.

 

[RHoch]

yea the code is a P1689. no comm between ECM and inj pump mod.