Fuel rail pressure sensor codes

How its codes differ

• P0191 is a plausibility code for this sensor: the reading is in electrical range but does not fit what should be happening. That can mean the sensor or its wiring is wrong, or that the pressure really is wrong, so the sensor is not automatically the faulty part.
• P0089 is set against the pressure regulator on the high-pressure pump, but it relies on this sensor's reading. GM tells technicians on some 2014–2016 trucks, SUVs and Corvettes to replace the rail pressure sensor when published diagnostics do not find the fault.
• When P0087 or P0088 (pressure too low or too high) are stored with P0191, the pressure itself is more likely to be the problem than the sensor; GM bulletins link that pattern to fuel contamination and pump faults.

Codes

• P0089

  Fuel pressure regulator not holding the pressure the computer asks for

  Severity: Inspect soon

• P0191

  Fuel rail pressure sensor reading does not make sense

  Severity: Inspect soon

Signs it's failing

• Check engine light with P0191 or P0089
• Hard starting, stalling or no start
• Loss of power or hesitation
• Poorer fuel economy

How to test it

1. Read all stored codes and note whether they are active or only in history; GM warns against replacing fuel parts for a code that is only in history. (Low risk)

2. With a scan tool, look at rail pressure with the key on and engine off and compare actual with desired pressure at idle. A reading that jumps when the sensor harness is moved points to wiring. (Use caution)

   Warning: Keep hands, hair, clothing and tools clear of the fan and belts while the engine is running, and do not run the engine in a closed garage. Do not loosen any fuel fitting.

3. Checking the sensor against a known pressure, testing its circuits and replacing it are jobs for a shop. (Best left to a shop)

   Warning: On direct-injection engines the rail holds very high pressure, and it can stay pressurised after the engine is switched off. A fuel spray can cause injury and fire.

After the repair

• Recheck actual against desired rail pressure at idle and as engine speed rises: they should track closely.
• Confirm no fuel smell or wetness around the sensor after it was replaced.
• Clear codes only after the repair, then drive normally over several days with both city and highway driving so the readiness monitors can complete; clearing codes or disconnecting the battery resets them to not ready, which fails an emissions test.