ECM Advice

[97charger]

2001 Dodge 2500-manual trans. Problem started when I lost prime voltage to lift pump CEL (check  engine light P1693 code) power supply wire tested at 8.2 volts in the start prime position but I had good voltage in run. Sent ECM in for testing repairs. 
-Repaired/tested ECM had good lift pump voltage after repairs, no codes or CEL but severely delayed throttle response to the point it was un-drivable. Tested APPS as per Mopar1973 posts.  
-ECM Vendor provided replacement rebuilt ECM, Truck runs, good voltages to lift pump, as soon as I pull onto the road I get CEL/MIL P1693 code unable to pull any other sub codes. Used 3 different OBD II scanners with nothing. 
-Replacement ECM #3, Good voltage to lift pump. Upon starting truck races to 2200 RPM and erratically bounces between idle and redline without touching throttle. CEL P0123 and P0121 codes. Followed diagnostic/testing for P0121 code, replaced APPS.  With all 3 ECM’s I’m getting .51 volts increases with throttle advancing.

 

Am I wrong thinking this is an an ECM issue or am I dealing with something else? 3 ECM’s different symptoms and issues. 

Edited August 27 by 97charger
Updated

[Great work!]

Try doing the APPS calibration. Search this site for the procedure. It easy to do.

 

Good battery connections and grounds are required on thees trucks.

 

Check the ECM connector carefully for pin sockets that may have pushed back into the plastic, that can cause a bad connection. 

[97charger]

Did all this day 1, 7 weeks ago when the issue started and daily now every time I’m troubleshooting it.  I have cleaned every ground I can locate, inspected and cleaned the ECM pins every time I’m swapping ECM’s with CRC electrical cleaner and canned  air. I do the APPS calibration and relearn after every ECM swap. I have been swapping the ECM out 2-3 times a day for the last 3 weeks after checking, testing, cleaning, replacing things. 

[Tractorman]

On 8/19/2024 at 4:23 PM, 97charger said:

-ECM Vendor provided replacement rebuilt ECM, Truck runs, good voltages to lift pump, as soon as I pull onto the road I get CEL P1693 code unable to pull any other sub codes.

 

On this ECM, you say "truck runs".  Does this mean everything is normal and the truck runs good?  Just a 1693 code?  Does the code set the MIL (Malfunction Indicator Lamp)?

 

On 8/19/2024 at 4:23 PM, 97charger said:

Problem started when I lost prime voltage to lift pump CEL (check  engine light P1693 code) power supply wire tested at 8.2 volts in the start prime position but I had good voltage in run.

 

This could be normal lift pump voltage while the engine is cranking.   The ECM reduces voltage to the lift pump by using pulse width modulation during engine cranking to prevent possible hard starts under heat-soaked startups.  The ECM supplies full voltage to the lift pump after the engine is running.

 

Is you lift pump fuel system completely stock?  Does the ECM drive the lift pump directly?

 

- John

 

[97charger]

ECM #2 of the 3 I have, truck starts and drives great, MIL light is illuminated and P1693 code is present. I’ve been to 3 different shops who have tried searching for secondary codes but unable to find anything. Have an appointment for a fourth tomorrow. When scanning we are unable to reset the MIL light scanners don’t recognize it being illuminated. 

ECM stock supplies power directly to the lift pump. There are 2 outputs off the ECM (prime) in the start position provides voltage 10-20 seconds, second output provides voltage in the “run” position, they are spliced from the factory into a single wire providing power to the lift pump. I had a break in the wiring 5 years ago and lost all voltage completely. Replaced the wiring after the splice with better wiring and a new plug. When I initially was troubleshooting the low voltage issue 7 weeks ago I tested the 2 wires prior to the splice to determine it as ECM related. 

 

I am running a FASS System so the wire from ECM goes to a relayed circuit for the FASS system as the “signal/trigger” wire.  All 3 ECM’s give good voltage in start and run positions, and I have 17 PSI dropping to 15 under throttle. 

Edited August 27 by 97charger

[Tractorman]

Great detail on your reply. 

 

Another thought.  Have you tried using the key switch to read codes in the odometer display?  2001 is a questionable year for using the key switch to read certain codes.  Some 2001 models read the PCU only, and other models read PCU and ECU.  If your truck happens to read both, maybe you can see the companion code in the ECU.  If your truck shows both, just be sure to be patient and wait for both PCU and ECU to say "DONE".

 

 

Regardless, it does seem there is a hidden ECU code that needs to be seen.  Just don't know how to get there.

 

- John

Edited August 27 by Tractorman

[97charger]

Unfortunately mine is an early 2001 and the key trick only works for the PCM. I get P-1693, P-done and it goes back to the odometer. 

[97charger]

Truck is fixed. All 3 ECMs I was working with were sent out to Automotive Computer Specialists and they were able to send me back a repaired operational ecm. They sent me a lengthy printout out what was found wrong with the warrantied rebuilt ecm I purchased. While the ecm was being repaired I redid all battery connections all new military grade clamps, did the alternator wire mod, had alternator tested to eliminate excessive noise. Big thank you to Automotive Computer Specialists and Mopar1973man for all the advice and help