Diesel Trouble Codes

P1093 — Fuel Pressure Regulator Control Circuit Low (LB7 Duramax)

P1093 is a manufacturer-specific low rail pressure during power enrichment code for the LB7 Duramax (2001–2004) with Bosch CP3 pump, rail pressure sensor, and…

Updated September 2, 2026

What it means

The ECM has detected that the fuel pressure regulator control circuit voltage is lower than expected. On the LB7 Duramax this code is a manufacturer-specific low rail pressure during power enrichment condition that applies to this platform.1

Most likely causes

  1. Fuel pressure regulator control circuit electrical fault (wiring, connector, or ECM driver) causing low control voltage — The ECM monitors the regulator control circuit; a low voltage condition can be an electrical fault in the circuit that controls the fuel pressure regulator.21
  2. Fuel pressure regulator performance issue on the CP3 pump — The LB7 uses a Bosch CP3 high-pressure pump with a pump-mounted fuel pressure regulator. Regulator performance problems can contribute to rail pressure control faults.1
  3. Rail pressure sensor or circuit anomaly affecting regulator control feedback — Rail pressure sensor circuit faults can be confused with actual pressure issues from the CP3/regulator/injector return flow on this platform.3
  4. Excessive injector return flow / injector body leakage affecting rail pressure during enrichment — LB7 injectors are mounted under the valve covers and are a known weak point with return-flow/balance-rate drift; faults can present as rail pressure control issues.1

How to diagnose

  1. Verify code and freeze frame; confirm P1093 is present on LB7 Duramax (2001–2004) with CP3 pump and pump-mounted regulator.
  2. Inspect fuel pressure regulator control circuit wiring and connectors for damage, corrosion, or poor contact; check ECM driver output per circuit fault guidance.
  3. Monitor rail pressure sensor signal and compare to expected values; evaluate for sensor circuit high/low conditions that can be confused with mechanical pressure issues.
  4. Check fuel pressure regulator performance; regulator performance codes such as P0089 are relevant to this platform.
  5. Assess injector return flow and balance rates; LB7 injectors under valve covers are known for cracked bodies and return-flow drift affecting rail pressure.

Parts and tools you may need

Rough cost and difficulty

Diagnostic labor varies; parts costs depend on whether the fault is wiring/ECM driver, fuel pressure regulator, rail pressure sensor, or injector return issues.

When to see a pro

If rail pressure cannot be verified safely, or if high-pressure fuel system service is required, have a qualified diesel technician perform diagnosis and repair. Do not service high-pressure fuel lines without proper training and safety equipment.

Sources

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

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

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