Search Catalog

Bad ECM symptoms

A failing engine control module (ECM) on a Caterpillar, Cummins or Detroit Diesel engine usually shows one of the symptoms below. Most of them can also come from wiring, power or a sensor, so each one lists what to rule out first, and how to tell when it really is the ECM.

Jump to a symptom

Engine cranks but won’t start

The engine turns over normally but never fires. Often there is no injector signal, and sometimes the scan tool can’t reach the ECM either.

Rule these out first

  • Battery voltage while cranking, and the battery cables
  • ECM power and ground wires, fuses and relays
  • The ECM connectors: bent, pushed-back or corroded pins
  • Fuel supply and the crank / cam position sensors

Repair or replace

When it’s the ECM

If power and grounds are good at the ECM connector, the sensors check out and there is still no injector signal, the ECM itself has usually failed (often its power supply or injector driver circuit).

ECM repair from $399.99 Replacement ECMs

No communication with the ECM

Cat ET, Cummins INSITE, Detroit DiagnosticLink or your scan tool can’t connect to the engine ECM, while other modules on the truck may still show up.

Rule these out first

  • The diagnostic connector, adapter and cable
  • Datalink wiring (J1939 / J1708) and terminating resistors
  • Key-on power and grounds at the ECM

Repair or replace

When it’s the ECM

When the datalink and the ECM’s power and grounds test good but the ECM still doesn’t answer, the unit needs to be tested on a bench.

ECM repair from $399.99 Replacement ECMs

Engine stalls or shuts down while driving

The engine dies at random, often over bumps or when hot, then restarts after a while.

Rule these out first

  • Engine protection shutdowns (low oil pressure, high coolant temperature): check the active codes first
  • Loose or corroded connectors and a harness rubbing on the frame
  • The ignition switch and key-on power feed
  • Fuel supply and filters

Usually repairable

When it’s the ECM

Random shutdowns with no protection codes, that get worse with heat or vibration, often come from cracked solder joints or a failing component inside the ECM. That is usually repairable.

ECM repair from $399.99

ECM internal fault codes that keep coming back

Codes that point at the controller itself, for example J1939 SPN 629 (controller #1), Cummins fault code 111 (ECM critical internal failure), or CID / SID 254 on older Cat and Detroit engines. Many unrelated sensor codes at the same time can point to the ECM too.

Rule these out first

  • Clear the codes and see if they return
  • A shorted sensor or harness can pull down the ECM’s 5-volt sensor supply and set many codes at once: unplug sensors one at a time
  • Battery voltage and ECM grounds (low voltage sets false codes)

Repair or replace

When it’s the ECM

If the internal-failure code returns with good power and wiring, the ECM has to be repaired or replaced.

ECM repair from $399.99 Replacement ECMs

Loss of power, rough running or misfire on several cylinders

The engine runs rough, misses on a group of cylinders, smokes, or won’t pull, with injector circuit codes on more than one cylinder.

Rule these out first

  • Fuel filters, fuel pressure and air intake
  • Boost leaks and the turbo / VGT actuator
  • The injector harness and connectors (a single bad injector usually sets a code on one cylinder only)

Usually repairable

When it’s the ECM

Injector codes on several cylinders that stay with the ECM when the harness checks good point to a failed injector driver inside the ECM.

ECM repair from $399.99

Throttle not responding, stuck at idle, gauges or cruise acting up

The engine stays at idle or won’t rev, cruise control stops working, the tach or other gauges behave erratically.

Rule these out first

  • The accelerator pedal sensor and its wiring
  • The 5-volt sensor supply (see fault codes above)
  • The dash cluster and its datalink connection

Usually repairable

When it’s the ECM

With a good pedal sensor and wiring, an ECM that ignores the throttle signal needs to be bench tested.

ECM repair from $399.99

Problems after a jump start, welding or a wiring short

Trouble started right after jump-starting, welding on the truck, reversed battery cables or a short in the wiring.

Rule these out first

  • All fuses and fusible links
  • Battery cables, grounds and the main power feed to the ECM

Usually repairable

When it’s the ECM

A voltage spike or reversed polarity often damages the ECM’s power supply. That is a common repair.

ECM repair from $399.99

Water, corrosion, burnt smell or a damaged case

Water or oil got into the ECM or its connectors, there is green corrosion on the pins, a burnt smell, or the case is cracked.

Rule these out first

  • Corrosion on the connector pins only (the harness side can often be cleaned or repinned)
  • Don’t open the ECM case yourself

Usually replaced

When it’s the ECM

Liquid or burn damage inside the ECM often can’t be repaired, so a replacement is usually faster. We can still test your unit first.

Replacement ECMs

Repair or replace your ECM?

Both are done in our Fort Worth, Texas shop and come with a 1-year warranty.

Repair yours

From $399.99

  • You ship us your ECM; most repairs take 1–2 days once it arrives
  • You keep your own unit and its programming
  • Best when the truck can wait for shipping both ways
ECM repair prices

Replace it

  • Remanufactured and tested ECM matched to your part number
  • Programmed for your engine (Detroit: we transfer the programming from your original unit)
  • Best when the truck is down or the old unit has water or burn damage

Not sure?

  • Send it in: we test it on the bench
  • $149 diagnostic fee only if no problem is found or it can’t be repaired
  • We don’t diagnose over the phone, but we can tell you which unit fits
Call 726-999-0231

Symptoms by engine brand

More on diagnosing an ECM

Not sure which ECM you need?

Send us your engine model and serial number, or the part number on your ECM, and we'll tell you whether to repair or replace it, and what it costs.

Call 726-999-0231 Request a quote