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DTC codes / GM codes / P1290

P1290 · GMCNG Fuel Pressure Too High

P1290 on a GM compressed natural gas (CNG) vehicle means the powertrain control module (PCM) has detected that the fuel pressure in the CNG system is higher than the calibrated maximum for the current operating conditions. The PCM monitors the CNG pressure sensor circuit and sets this code when the signal indicates pressure has exceeded the safe threshold, often due to a stuck regulator or a sensor reporting falsely high pressure.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyProfessional
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Rough running or misfires under load if pressure is excessively high
  • Fuel smell or audible hissing from the CNG system in severe cases
  • Reduced engine power or limp mode if the PCM enters protection strategy
  • Hard starting or stalls after refueling, especially if the tank was overfilled

Common causes, most likely first

  1. Faulty CNG pressure sensor reading higher than actual pressure
  2. Stuck or failed CNG pressure regulator allowing tank pressure to pass through unregulated
  3. Restricted or kinked return line causing pressure to build in the low-pressure side
  4. PCM calibration issue or corrupted adaptive learning for the CNG system
  5. Wiring damage or corrosion in the CNG pressure sensor circuit causing a skewed signal
  6. Mechanical failure inside the CNG regulator assembly, such as a ruptured diaphragm

How to diagnose and fix it

  1. Connect a scan tool and verify the CNG pressure sensor reading in live data against a known-good mechanical gauge
  2. Inspect the CNG pressure sensor connector and wiring for corrosion, chafing, or loose pins, and repair as needed
  3. Check the CNG regulator for proper operation and confirm it is not stuck open or bypassing pressure
  4. Inspect the CNG return line and any pressure relief components for restrictions or blockages
  5. Perform a PCM relearn or calibration update if the pressure sensor and regulator test good
  6. Replace the CNG pressure sensor if it is skewed, then clear the code and verify the repair with a test drive
  7. Replace the CNG regulator assembly if it is confirmed faulty, following all CNG safety procedures

CNG pressure codes that mislead

  • A skewed CNG pressure sensor is the most common cause of P1290, and it often reads high even when the actual system pressure is normal, so always verify with a mechanical gauge before replacing the regulator.
  • Overfilling the CNG tank at a fast-fill station can temporarily raise pressure above the normal operating range and set this code, which may clear on its own after the vehicle sits and stabilizes.
  • The PCM may set P1290 as a companion code to P1291 or P1292 if the pressure sensor circuit has an intermittent fault, so check for other stored codes before diagnosing.
  • CNG systems operate at very high pressure, and any diagnostic step that involves opening the fuel system must follow manufacturer safety procedures and local regulations for natural gas vehicles.
  • A restricted CNG filter or a failing high-pressure lock-off solenoid can cause pressure to back up and trigger P1290, so inspect the entire fuel delivery path rather than just the regulator.

Can I keep driving with P1290?

You can drive the vehicle short distances to a repair shop, but avoid hard acceleration and refueling until the fault is diagnosed, because excessively high CNG pressure can damage components or create a safety hazard. If you smell gas or hear hissing, stop driving immediately and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage