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P1234

Injector Circuit Cylinder 5 Intermittent.

  • GMC
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
2
AreaFuel and air metering (injector circuit)
34
FaultThe specific fault in that area

What it means

On a GMC, P1234 means the engine control module has detected an intermittent fault in the fuel injector circuit for cylinder 5. The module monitors the injector driver and its wiring, and it saw a signal or voltage that was briefly out of the expected range rather than a constant failure. Because the fault comes and goes, the cylinder may misfire or run lean or rich for short periods.

Symptoms

  • Intermittent misfire or rough running, mainly on cylinder 5
  • Engine hesitation or stumbling under load or at idle
  • Check engine light on, possibly flashing during a misfire
  • Poor fuel economy or occasional fuel smell
  • Occasional hard starting or momentary loss of power

Possible causes

  • Loose, corroded or damaged connector at the cylinder 5 injectorlikely
  • Chafed, stretched or intermittently open or shorted wiring between the injector and the control modulelikely
  • Fuel injector with an intermittent internal winding fault (resistance changes when hot or vibrating)likely
  • Poor power or earth supply to the injector circuit, such as a corroded connection or a fault in the injector feedpossible
  • Corroded or loose pins at the control module connectorpossible
  • Internal fault in the engine control module injector driverrare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data (engine temperature, load, speed) to see when the fault occurred
  2. Check for other injector or misfire codes to see whether the fault is isolated to cylinder 5
  3. Inspect the cylinder 5 injector connector and harness for damage, corrosion, bent or loose pins, heat damage and rubbing on engine parts
  4. Wiggle-test the harness and connector with the engine running and watch for changes in idle quality or live misfire data
  5. Measure the cylinder 5 injector resistance cold and again when warm, and compare with the specification for that engine
  6. Check the injector feed voltage and earth supply, and test the wiring for continuity and shorts to earth or voltage
  7. Use a suitable test lamp or scope to check the injector pulse from the control module while the fault is present
  8. Inspect the control module connector pins, and only suspect the module after wiring and injector are proved good; the layout depends on model and engine

How to fix

  • Clean, repair or replace the damaged injector connector or terminals
  • Repair or replace the faulty section of wiring, protecting it from rubbing and heat
  • Replace the cylinder 5 injector if its resistance or operation is out of specification
  • Restore the injector power or earth supply by repairing the faulty connection or fuse circuit
  • Repair the control module connector pins if corroded or loose, and replace or repair the module only if it is confirmed faulty
  • Clear the codes after the repair and road test to confirm the fault does not return

Can I keep driving?

Medium severity

The car can usually be driven for a short time to get it repaired, but the misfire may worsen. Avoid heavy loads and long journeys, and stop if the warning light flashes, as unburnt fuel can damage the catalytic converter.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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