1993 Cummins N14 ECM issues

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Opus62, Oct 25, 2019.

  1. Opus62

    Opus62 Bobtail Member

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    Oct 25, 2019
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    HI. This is my first post in this forum so please forgive any screw ups on my part.
    Full disclosure: I am not a qualified Cummins diesel mechanic but I have been given the task of maintaining my employer's 1993 Freightliner dump truck. [I work for an equipment rental company/contractor]

    Now on to the meat of the matter. The engine is an N14 that seems to run well. But in recent months it has seen fit to derate itself with a yellow and flashing red light on the dash. Quckserv on the Cummins web site has been most helpful. The trouble codes are 123, 141, 145, 154, 213, 352, 415 and 422. Everything seems to relate to code 352, low voltage [0.5 volts] at pins 2,3,5,12,21 and 22 of the sensor harness. Pin 10 of the OEM harness, however, does have 4.5 - 5.0 volts. At all connectors at the sensors I am getting 0.3 to 0.6 volts. As for code 422, coolant level sensor, there is no such sensor on this truck. After unplugging all sensors and the shorting plug at the coolant level sensor plug I still get the 352 code and still only get low voltage. It's looking a lot like the 5 volt supply to the sensor harness is dead. My big question is, can I tap off of the 5 volt supply coming from pin 10 of the OEM harness or can I add on an external 5 volt source to the 5 volt circuit in the sensor harness? Tight budgets preclude taking the truck to the Cummins distributor for a proper check over.

    Thankyou in advance for ANY advice.
     
    Last edited: Oct 25, 2019
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  3. BoxCarKidd

    BoxCarKidd Road Train Member

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    What is your alt voltage? Check grounds! There is a search block on the top right of your screen. Some you tube N14 stuff is pretty good.
    When wiring starts being cobbled up like that it is the beginning of of a long term on going nightmare. Boss is better to send to out for repair if needed. Finding someone to trust is hard.
    I wish I had just told a boss that 34 years ago on a job. He keep pushing me.
    Well do the best you can do, you have all day.
    I did not have training on those. They did not have the equipment to test it. The vehicle broke down and the driver had to walk. Then I was dirt.
    If you were working on my vehicle I would request you take some time and work through the simple stuff. But please do not go jumping wires.
    JMHO and good luck. There are some people on here that can help you a lot. They have helped me tremendously. Work on that and let us know.
     
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  4. Bones3

    Bones3 Bobtail Member

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    First of all, I would check the main power to the ecm. There should be 2 fuse holders connected directly to the batteries positive terminal, and the other ends go to the ecm. These wires and fuse holders get corroded over time and should be checked, cleaned or replaced to make sure the ecm has a good clean supply voltage of 12 volts. Also make sure the engine, ecm, and frame are well grounded to the negative battery terminals. Then check your 5 volts coming out of the ecm at the various pins with no sensors connected.
     
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  5. Opus62

    Opus62 Bobtail Member

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    Just like you, I am unqualified and we don't have any of the special tools and testers needed. And, like you, miracles were/are expected.
     
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  6. x1Heavy

    x1Heavy Road Train Member

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    Miracle man over here. But not on something I cannot see and touch.

    Please whatever you do don't go jumping wires. Use the ones the factory gave you. What always happens is you jump wires, whala shes alive and 6 months later jump more of the same until there is a ball of wire smoking in the mass pile.

    If that truck is sick enough to visit hospital, er dealership then let them have at it. They would likely be overjoyed to work on a museum antique rather than the over engineered computer stuff today.
     
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  7. AModelCat

    AModelCat Road Train Member

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    Majority of electrical faults are related to the wires. Sensors are more likely to fail than ECM's. ECM itself is usually pretty bulletproof. The last thing listed in most troubleshooting procedures is the ECM.

    Being that the truck is 26 years old, I would start with a thorough inspection of the engine harness, plugs etc. Pay close attention to anything that doesn't look "original". Most wiring failures are from previous repairs/alterations.

    I wouldn't tap into another power source. Sometimes the ECM reads voltages being sent/received in order to determine fault conditions.

    Also verify that the ECM is getting keyed power, constant power and ground on all applicable pins.
     
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  8. Opus62

    Opus62 Bobtail Member

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    Believe me, the LAST thing I want to do is modify any wiring, mainly because *I* will be the poor schmuck who has to go back and fix it again. It would be a "hail Mary" play to win the cup.
     
  9. pup

    pup Light Load Member

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    Call Midwest ECM repair. He can tell you if your problem is likely the ecm or not. He'll repair your ecm or exchange it. Better quality than Cummins & much less expensive.
     
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  10. 18 wheels of fury

    18 wheels of fury Light Load Member

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    I have a Cummins isx and a code reading sensor supply voltage it deratred on me got it to a shop and it ended up being the pressure sensor...there's like 5 sensors that work on circuit 1 so the truck shows different codes but this guy knew about it and I was back on the road in a hr
     
  11. BoxCarKidd

    BoxCarKidd Road Train Member

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    Glad you found a good guy. I thank you should do him a favor? and post his shop.
     
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