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P1237

Cylinder 1 Injector Circuit Open Circuit.

  • Volkswagen
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
2
AreaFuel and air metering (injector circuit)
37
FaultThe specific fault in that area

What it means

On Volkswagen, P1237 means the engine control unit has detected an open circuit in the cylinder 1 injector circuit. The control unit monitors the injector driver circuit and found no current path, so the injector is not being driven as commanded. The fault can be in the injector, its wiring and connector, or the control unit itself.

Symptoms

  • Engine management light on
  • Misfire or rough running, especially on cold start
  • Cylinder 1 not firing, giving a noticeable loss of power
  • Hard starting or extended cranking
  • Increased fuel consumption or fuel smell from unburnt fuel
  • Car may run in a reduced-performance mode

Possible causes

  • Faulty cylinder 1 injector with open-circuit coillikely
  • Corroded, loose or damaged injector connector terminalslikely
  • Broken or chafed wiring between the injector and the control unitpossible
  • Poor power supply or earth to the injector circuit, such as a relay or fuse issue (depends on model and engine)possible
  • Wiring harness damage from heat, vibration or previous repair workpossible
  • Faulty engine control unit injector driver stagerare

How to diagnose

  1. Read all stored codes and freeze frame data, noting engine temperature, load and whether the fault is current or intermittent
  2. Visually inspect the cylinder 1 injector connector and nearby harness for damage, corrosion, oil contamination or poor routing
  3. Disconnect the connector and check the terminals for tightness, bent pins and moisture, then refit firmly
  4. Measure injector coil resistance and compare with the manufacturer specification for your engine
  5. Check the supply voltage and earth or switched signal at the injector connector with the ignition on and while cranking
  6. Wiggle-test the harness with the engine running or on live data to see if the fault appears or misfire changes
  7. Test wiring continuity and insulation between the injector connector and the control unit connector, following the wiring diagram for your model
  8. Swap the injector with another cylinder temporarily to see whether the fault follows it, if access allows

How to fix

  • Replace the cylinder 1 injector if its coil is open circuit or out of specification
  • Clean or repair the injector connector, or replace the connector and terminals if corroded or damaged
  • Repair or replace the damaged section of wiring, using proper soldered and sealed joints
  • Restore the power supply or earth by repairing the fuse, relay or related connection where one is at fault
  • Replace or repair the engine control unit only after wiring and injector faults are fully ruled out

Can I keep driving?

Medium severity

The car can usually be driven short distances, but cylinder 1 is not being fuelled properly, so avoid long trips. Unburnt fuel can overheat and damage the catalytic converter, so have it repaired soon.

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

This code for other makes

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