Diesel Trouble Codes

P008A — Low Pressure Fuel System Pressure Too Low (6.7 Cummins (SCR / DEF))

Low Pressure Fuel System Pressure Too Low

Updated September 2, 2026

What it means

The PCM is seeing low-side (supply) fuel pressure below expected on the 6.7L Cummins SCR/DEF 2013–present. This is a low-pressure supply fault, not a high-pressure rail pressure fault. Platform uses an in-tank electric supply pump/module and a CP3 (2013–2018, 2021+) or CP4.2 (2019–2020) high-pressure pump with rail pressure sensor, FCA/MPROP and mechanical rail pressure relief/limiting valve. VGT HE300VG with electric actuator, no wastegate/vacuum/boost solenoid; EGR+cooler, DOC/DPF/SCR; grid heater, no glow plugs; mechanical thermostat; gear-driven timing; MAP primary air metering.1

Most likely causes

  1. In-tank electric supply pump / fuel module degraded or failing — Low-side supply pressure drops under load or at idle; may set P008A and can contribute to high-pressure rail under-supply. Typical on 6.7L Cummins SCR/DEF with in-tank electric supply pump.1
  2. Restricted fuel supply / clogged filter or pickup — Restricted flow from tank pickup screen, fuel filter, or lines reduces low-side pressure to the CP3/CP4.2. Diagnose by checking supply pressure and flow per service data.1
  3. Air ingress on low-pressure side — Leaks at connections, seals, or module allowing air into supply causes pressure loss and erratic low-side readings.1
  4. Faulty low-pressure fuel pressure sensor / wiring — Erroneous sensor signal can cause PCM to report low pressure even with adequate supply. Verify sensor reading vs actual supply pressure.1

How to diagnose

  1. Verify freeze frame and repeatability of P008A under load and idle.
  2. Inspect in-tank supply pump/module electrical supply and connectors; check for codes related to pump circuit.
  3. Check low-side fuel pressure with a suitable gauge at the supply test point per service information; compare to spec at idle and under load.
  4. Inspect fuel filter condition and replace per interval; check tank pickup screen and lines for restriction or contamination.
  5. Perform leak/air-ingress test on low-pressure side; inspect seals, connections, and module for air entry.
  6. If supply pressure is within spec but code persists, evaluate low-pressure fuel pressure sensor and wiring for faults.
  7. Do not confuse with high-pressure rail codes such as P0087; P008A is low-side supply. Platform-specific hardware: CP3 2013-2018 & 2021+, CP4.2 2019-2020; in-tank electric supply pump; rail pressure sensor + FCA/MPROP + mechanical rail relief valve.
  8. Document findings and clear codes after repairs; retest drive cycle to confirm.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by model year and configuration. In-tank pump/module and fuel filter are common service items; diagnosis requires pressure testing before parts replacement.

When to see a pro

If low-side pressure remains low after filter and basic checks, or if high-pressure pump/rail symptoms appear, have a qualified diesel technician evaluate the supply system and high-pressure components. Do not service high-pressure fuel lines without proper training and safety equipment.

Sources

  1. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

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