The C15 ECM failures we see most

The 6NZ is the most-searched Cat ECM there is, and it fails the same three ways over and over.

Dead cylinder that survives an injector swap

What you see: One hole down on the cutout test, a miss under load, a derate. You replaced the injector and it is still there.

What's happening: The injector driver inside the ECM has failed. On 6NZ and MBN modules this is the number-one fault.

What we do: We rebuild the driver stage and bench-fire all six channels before it ships.

Runs, but Cat ET will not connect

What you see: The truck runs and drives but no diagnostic tool will talk to the ECM. You cannot read or program it.

What's happening: The J1939/ATA data-link circuit in the module has failed.

What we do: We restore communication on the bench so the module can be read and programmed again.

No power-up after a jump start or welding

What you see: Dead ECM after a jump, a battery swap, or welding on the frame. Sometimes intermittent first.

What's happening: Overvoltage took out the internal supply or protection components.

What we do: We repair the supply section at the component level and load-test the module before it goes back.

ACERT: intermittent codes and derates

What you see: MXS/NXS/SDP units with codes that come and go with heat, or a derate nobody can pin to a sensor.

What's happening: Cracked solder joints or a failing regulator in the 120-pin ADEM 4 module.

What we do: We reflow and repair the failed section and thermal-cycle it on the bench.

Don't see your exact symptom? Send it in anyway. We bench-test every unit before we tell you what's going on, and if we fix it the diagnostic cost you nothing.

C15 arrangements and ECMs we repair

Give us your engine serial prefix and we know which module you have.

ArrangementECM generation / connectorOur bench
6NZADEM III, 70-pin (206-2700, 10R-4090)2 days
MBNADEM III, 70-pin2 days
BXS (early ACERT)ADEM III, 70-pin (256-1159, 10R-4094)2 days
MXS, NXS, SDP (ACERT)ADEM 4, 120-pin (255-5287)about a week

How the repair goes

  1. 1

    Ship it in

    Self-ship free, or add a prepaid UPS label. Drop-offs in Princeton, MN by appointment. Include your engine serial number.

  2. 2

    We test it

    $350 bench fee, credited toward the repair. We tell you exactly what failed, usually within a day of receipt.

  3. 3

    We fix it

    Injector driver repair, communication restoration, power-supply and 5-volt sensor supply repair, parameter recovery, whatever it needs. 2 days on the bench.

  4. 4

    Back to you

    Programmed to your engine, every channel bench-tested, 2-year warranty. Status email at receipt, at diagnosis, and at ship.

C15 exchange units we stock

If yours is beyond repair, or the truck can't wait: remanufactured, bench-tested, programmed to your engine serial, 2-year warranty. Usually ships the same day.

Questions we get on C15 ECMs

How much does a C15 6NZ ECM repair cost?

$745 flat with the bench fee included. The $350 bench-test fee you pay at checkout credits 100% toward the repair. If we cannot repair it we tell you first and offer a tested 6NZ exchange unit with the bench fee credited.

How long does a C15 ECM repair take?

6NZ, MBN and BXS 70-pin units are 2 days on the bench plus 1-3 days return shipping. 120-pin ACERT (MXS, NXS, SDP) about a week.

Do I need to send my engine serial number?

Yes. We program the repaired ECM to your engine serial before it ships so it plugs in and runs.

Is a 6NZ ECM worth repairing, or should I buy one?

Repair at $745 is almost always the better deal on a working truck, and it keeps your own parameters. If yours is beyond repair, or the truck cannot wait, we stock tested 6NZ and MBN exchange units.

Related: Cat 70-pin ECM problems & symptoms · 3406E ECM repair · C12 ECM repair · C10 ECM repair

Verified Google reviews

What truck owners & shops say

★★★★★
"Mike does great work and sent my repaired ECM back to me right away. Saved me thousands of dollars vs. using the dealer. Would recommend to anyone that needs prompt repair."
Michael B. via Google
★★★★★
"From ECMs and harnesses to straight-out cutting counter bores in-frame for us. Great shop — and a great person to have in your pocket."
Mega24v via Google
★★★★★
"Highly recommend these guys! Fast turnaround — I had my ECM back and repaired by the next day. Will definitely do more business in the near future."
Javon Z. via Google
★★★★★
"Michael is a diesel guru. He made my rig scream and had it done when he said, for the price we agreed to. I'd highly recommend him."
Glenn S. via Google
★★★★★
"Mike is highly knowledgeable in all areas of diesel repair — from mechanical work to advanced electrical diagnostics. You can count on him to get the job done right."
David F. via Google
★★★★★
"Mike is a very professional and skilled mechanic. I highly recommend him for any of your needs."
Justin N. via Google

Read more reviews & leave your own →

Email us about a problem unit.

It comes straight to our inbox. A diesel tech reads it and answers, usually the same business day. Tell us the engine and what it's doing, and we'll let you know whether we can help.

Email us [email protected]

Send a quick question

Two fields. Goes to our inbox; we reply by email.