P0651 on 2017-2019 GMC Terrain: Sensor Reference Voltage 'B' Circuit Fault Explained

What's Unique About the 2017-2019 Gmc TERRAIN

For the 2017-2019 GMC Terrain and its platform mates like the Chevy Equinox, P0651 is rarely an isolated electrical fault. It is most often a companion code to P06DE (Engine Oil Pressure Control Solenoid Valve Stuck Off). A key manufacturer Technical Service Bulletin (TSB #PIP5247A) explicitly states that if P0651 is present with P06DE, technicians must diagnose P06DE first. The underlying cause is frequently a mechanical failure in the oiling system, such as debris in the oil pump's check valve or broken piston oil cooling nozzles (squirters), which creates an electrical fault in the oil pressure control system that the ECM interprets as a reference voltage problem.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: The 2017 model year is the final year of the first-generation Terrain, while 2018-2019 models belong to the second generation. However, the provided TSBs cover engines like the 1.5L and 2.0L LTG which are common across this year range, and the P0651/P06DE issue affects both generations depending on the installed engine.

Symptoms You May Notice

• Check Engine Light is on
• Engine running rough or stalling
• Reduced engine power (limp mode)
• Poor fuel efficiency
• Hesitation during acceleration
• Hard starting or no-start condition

Most Likely Causes

1. Fault related to DTC P06DE (Oil Pump/Pressure Control) 🔴 High Probability As per TSB #PIP5247A and TSB #PIP5676A, P0651 is a direct symptom of P06DE. The cause for P06DE can be foreign material in the oil pump's cold start checkball, a faulty oil pump assembly, or even broken internal plastic parts from piston oil squirters contaminating the oil pan and pump pickup.
   How to confirm: Scan for other codes. If P06DE is present, follow the diagnostic procedure for that code first. 🎬 See how to diagnose and fix P06DE step-by-step This involves checking engine oil pressure with a mechanical gauge and dropping the oil pan to inspect the oil pump assembly and pickup tube for debris or broken plastic pieces.
   Typical fix: If debris is found in the oil pump check valve, cleaning it may resolve the issue. If broken piston oil squirter parts are found, they must be replaced. Often, the entire oil pump assembly (which is part of the balancer assembly) must be replaced.
   Est. part cost: $200-$400 for an oil pump assembly.
2. Damaged Wiring Harness 🟡 Medium Probability Wiring can become chafed, corroded, or pinched, especially in areas where the harness is routed near the engine and transmission. A short to ground on the 5-volt reference circuit will trigger this code.
   How to confirm: Visually inspect the wiring harness for any signs of damage. Pay close attention to the harness sections for sensors on the 'B' circuit (e.g., Crankshaft Position Sensor, APP sensor). A multimeter can be used to check for continuity and shorts to ground.
   Typical fix: Repair the damaged section of the wire or replace the affected harness.
   Est. part cost: $10-$100 for wiring repair supplies.
3. Faulty Sensor on the 'B' Circuit ⚪ Low Probability A sensor on the 5-volt reference circuit can short internally, pulling down the voltage for all other sensors on that circuit. While possible, on this platform it's less common than the P06DE-related issue.
   How to confirm: With the key on and engine off, unplug sensors on the 'B' circuit one by one (start with the oil pressure sensor if P06DE is present). If the 5-volt reference returns to normal after unplugging a specific sensor, that sensor is faulty.
   Typical fix: Replace the faulty sensor.
   Est. part cost: $50-$200 depending on the sensor. An oil pressure sensor replacement costs between $190 and $264 on average.

Rare But Worth Checking

• Faulty Engine Control Module (ECM): This is a rare cause. The ECM should only be considered after all other possibilities, including wiring and sensors, have been exhaustively checked and ruled out.
• Broken Piston Oil Cooling Nozzles (Squirters): A more serious mechanical failure mentioned in TSB PIP5247A. Plastic parts from the nozzles break off, fall into the oil pan, and get sucked into the oil pump pickup tube, causing oil starvation and triggering P06DE, which in turn triggers P0651.

Diagnosis Steps

1. Connect an OBD-II scanner and check for all stored diagnostic trouble codes.
2. If P06DE is present along with P0651, prioritize the diagnosis for P06DE as instructed by TSB #PIP5247A.
3. Follow the diagnostic procedure for P06DE. This involves checking oil level and condition, then potentially removing the oil pan to inspect the oil pump, its internal check valve, and the oil pickup tube for debris or broken plastic parts from piston oil squirters.
4. If P0651 is present alone, identify which sensors are on the 5-volt reference 'B' circuit using a service manual (likely includes Crankshaft Position Sensor, Accelerator Pedal Position Sensor, and Oil Pressure Sensor).
5. Visually inspect the wiring harness for those sensors for any signs of damage, corrosion, or loose connections.
6. Use a multimeter to check for a 5-volt signal at each sensor connector on the 'B' circuit.
7. If the voltage is low or absent, disconnect the sensors one by one. If the voltage returns after disconnecting a sensor, that sensor is likely shorted and needs replacement.
8. If no faulty sensor is found, check the wiring harness for shorts to ground or open circuits.
9. If all wiring and sensors are confirmed to be good, the final step would be to test the ECM itself, though this is the least likely cause.

Parts You'll Likely Need

• Engine Oil Pump / Balancer Assembly (OEM #12709993) — This is the most common fix when P0651 is accompanied by P06DE, as debris in the pump or a faulty pump itself is the root cause. The pump is often replaced as a complete assembly with the balance shafts. 🎬 Watch: Walkthrough of an Equinox oil pump replacement
  Trusted brands: ACDelco, Melling
  OEM price range: $300-$500
  Aftermarket price range: $200-$400

Related Codes That Often Appear With This One

• P06DE — Per manufacturer TSB #PIP5247A, these codes are directly linked. P06DE relates to the engine oil pressure control and is almost always the root cause of P0651 on this platform.
• P0521 — This code for 'Engine Oil Pressure Sensor/Switch Range/Performance' can also appear alongside P06DE, further indicating a problem within the oil pressure system.

Technical Service Bulletins (TSBs) & Recalls

• PIP5247A: Service Engine Soon Malfunction Indicator Lamp. Technician may find Diagnostic Trouble Code P06DE set in the Engine Control Module. P0651 may also be set in the ECM with the P06DE. Diagnostics may lead to finding broken piston oil nozzle/squirter parts in the oil pan.
• PIP5676A: MIL Due To P06DE and may also have P0521. Cause may be foreign material stuck between the cold start checkball and its seat in the oil pump.

Platform-Specific Known Issues

• TSB #PIP5247A: Explicitly links P0651 with P06DE and directs technicians to diagnose P06DE first. It also mentions that broken piston oil squirters can be a cause, leading to debris in the oil pan.
• TSB #PIP5676A: Details the diagnosis for P06DE, pointing to foreign material stuck in the oil pump's cold start checkball as a likely cause. Instructs technicians to clean the checkball or replace the entire balancer/oil pump assembly if no debris is found.