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P1243

Injector Circuit Cylinder 8 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)
43
FaultThe specific fault in that area

What it means

P1243 on a GMC means the engine control module detected an intermittent fault in the fuel injector circuit for cylinder 8. The module monitors the injector driver circuit and saw a brief open circuit, short or unexpected voltage that came and went rather than staying present. Because the fault is intermittent, the cylinder may run normally for long periods between events.

Symptoms

  • Check engine light on, possibly flashing if a misfire occurs
  • Intermittent misfire or rough running, especially at idle
  • Occasional hesitation or loss of power under load
  • Hard starting or momentary stumble
  • Slightly worse fuel economy
  • Code may clear itself and return later

Possible causes

  • Loose, corroded or damaged connector at the cylinder 8 injectorlikely
  • Chafed, stretched or heat-damaged wiring in the cylinder 8 injector harness, intermittently open or shorting to ground or voltagelikely
  • Faulty cylinder 8 injector with an intermittent internal coil faultpossible
  • Poor terminal tension or corrosion at the engine control module connector or a harness jointpossible
  • Intermittent power or ground supply problem to the injector circuit, such as a loose ground or a fault in the fuse or relay feedpossible
  • Internal fault in the injector driver within the engine control modulerare

How to diagnose

  1. Read the stored and pending codes and note the freeze frame data (engine temperature, load, speed) to see when the fault occurs.
  2. Check for other injector or misfire codes to confirm the problem is limited to cylinder 8.
  3. Visually inspect the cylinder 8 injector connector and harness for damage, rubbing, oil contamination, heat damage or loose fit.
  4. With the engine running, gently wiggle the connector and harness while watching for a change in idle quality or live misfire data.
  5. Measure injector coil resistance at the cylinder 8 injector and compare it with the specification for your engine, and with other injectors.
  6. Check the injector feed voltage and ground, and the related fuse and relay, using the wiring diagram for your model and engine.
  7. Use an injector-compatible test light or a scope to check for a proper switching signal on the cylinder 8 control wire, including when the fault appears.
  8. Check the module connector pins for corrosion or poor tension, and only suspect the module after wiring and the injector have been ruled out.

How to fix

  • Clean, refit or replace the cylinder 8 injector connector if it is loose or corroded.
  • Repair or replace the damaged section of injector wiring, using proper soldered and sealed joints rather than twisted splices.
  • Replace the cylinder 8 injector if its resistance or switching signal is out of specification.
  • Repair the faulty power or ground connection, or replace the faulty fuse or relay feeding the injectors.
  • Repair the module connector terminals, or replace or reprogram the engine control module only if a confirmed internal fault is found.

Can I keep driving?

Medium severity

The vehicle can usually be driven for a short time to reach a workshop, but get it fixed soon. If the engine light flashes or it misfires badly, reduce load and stop driving, 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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