Diesel Trouble Codes

P0202 — Injector Circuit Malfunction Cylinder 2 (LB7 Duramax)

P0202 on the LB7 Duramax means the ECM has detected an electrical fault in the fuel injector circuit for cylinder 2. The LB7 uses Bosch injectors mounted under…

Updated September 2, 2026

What it means

The engine control module has detected an electrical fault in the fuel injector circuit for cylinder number two. On the LB7 Duramax, injectors are Bosch units mounted under the valve covers and are a well-known weak point (cracked bodies, return-flow/balance-rate drift); faults show as P0201–P0208, misfire P0300/P030x, and rough running/fuel in oil/white smoke.1

Most likely causes

  1. Open or high resistance in the injector harness or connector at cylinder 2 — Inspect the under-valve-cover injector sub-harness and external engine harness for chafing, oil intrusion, or loose pins at the cylinder-2 injector connector. Compare circuit continuity and resistance to the other cylinders.1234
  2. Failed or internally shorted injector solenoid on cylinder 2 — A Bosch LB7 injector with an electrical fault can set P0202. Electrical testing of the injector coil resistance and isolation from ground can help differentiate a wiring issue from an injector failure.1
  3. ECM driver fault for cylinder 2 injector — If the wiring and injector test good, the ECM’s injector driver for cylinder 2 may be suspect. Verify power/ground and control signals at the ECM connector before condemning the module.1
  4. Oil contamination/corrosion in the under-valve-cover connector — LB7 injector connectors sit under the valve covers. Oil intrusion or corrosion can cause intermittent high resistance or shorts on the cylinder-2 circuit.1

How to diagnose

  1. Verify the code and freeze-frame data; confirm P0202 is current and note engine conditions at set.
  2. Visually inspect the engine harness and under-valve-cover injector sub-harness for chafing, oil, or damage, focusing on cylinder 2.
  3. Perform a pin drag test and continuity check of the cylinder-2 injector circuit from ECM to injector connector; compare to adjacent cylinders.
  4. Measure injector solenoid resistance at the injector connector and compare to spec and to other cylinders; check for short to ground or power.
  5. Inspect ECM connector pins for corrosion or oil intrusion and verify ECM power/ground supplies.
  6. If wiring and injector test normal, monitor injector command and feedback with a scan tool during cranking/running to isolate an ECM driver issue.
  7. Clear codes and retest after repairs; monitor balance rates and misfire counts for cylinder 2.

Parts and tools you may need

Rough cost and difficulty

Diagnostic labor varies; injector replacement on LB7 requires valve-cover removal and is labor intensive. Parts cost depends on whether the issue is wiring, connector, or a Bosch injector. Always confirm with testing before replacing components.

When to see a pro

If the fault persists after harness/connector verification, or if injector replacement is required, have a qualified diesel technician perform the work. Under-valve-cover access and high-pressure fuel system safety require experience.

Sources

  1. Curated DTC seed — LB7 Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — LB7 Duramax (curated) ↩︎

  3. Curated DTC seed — LB7 Duramax (curated) ↩︎

  4. Curated DTC seed — LB7 Duramax (curated) ↩︎