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DTC codes / P26xx · Computer and output circuits / P262C

P262CSensor Reference Voltage G Circuit / Open

P262C indicates that the engine control module (ECM) has detected an open circuit or out-of-range voltage on the sensor reference voltage G circuit, which is a 5-volt supply shared by multiple sensors. The ECM monitors this line and sets the code when the voltage drops below or rises above the expected operating range, often due to a wiring fault or a failed sensor internally shorting the reference line.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light (malfunction indicator lamp) with no other obvious symptoms
  • Rough idle or hesitation if the affected sensors include the throttle position or manifold absolute pressure sensor
  • Poor fuel economy or reduced engine performance due to incorrect sensor readings
  • Intermittent stalling or difficulty starting in some cases
  • Transmission shift quality issues if the reference voltage feeds a transmission sensor
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Open or damaged wire in the sensor reference voltage G circuit (broken, chafed, or corroded)
  2. Poor electrical connection at a sensor or ECM connector (loose pins, corrosion, or water intrusion)
  3. A sensor internally shorted to ground or to voltage on the reference G line, pulling the shared 5-volt supply down
  4. Failed ECM driver for the reference voltage G output (rare but possible)
  5. Aftermarket accessories or poor previous repairs tapping into the reference circuit
  6. Heat damage or vibration causing an intermittent open in the harness

How to diagnose and fix it

  1. Connect a scan tool and record all stored and pending codes, then check freeze-frame data to see the conditions when P262C set
  2. Inspect the engine wiring harness and connectors for the sensors that share the reference voltage G circuit, looking for chafing, corrosion, or loose pins
  3. Measure the reference voltage at each sensor connector with the key on, engine off; a healthy circuit should show close to 5 volts, and any deviation indicates a fault
  4. Disconnect sensors one at a time on the shared reference G line and recheck the voltage; if it returns to normal with a sensor unplugged, that sensor is internally shorted
  5. Perform a voltage drop test on the ground and power sides of the affected sensors to rule out ground-side issues that can mimic a reference voltage fault
  6. If the wiring and sensors check out, test the ECM reference voltage output directly at the ECM connector; if the voltage is missing there, the ECM may be faulty
  7. Repair or replace the faulty wiring, connector, or sensor as needed, clear the codes, and verify the repair with a test drive and live data review

Shared 5-Volt Reference Circuit Traps

  • The reference voltage G circuit often feeds multiple sensors, so a single shorted sensor can pull down the voltage for all of them and set codes for unrelated sensors; always check every sensor on the shared line.
  • A common misdiagnosis is replacing the ECM when the real problem is a chafed wire behind the engine block or near a heat source, so a thorough visual inspection of the harness is essential before condemning the module.
  • Intermittent opens can be caused by a broken wire inside intact insulation, which only shows up when the engine moves or the vehicle hits a bump; wiggle testing the harness while watching live data can reveal these.
  • Aftermarket electrical accessories, such as alarm systems or add-on gauges, are often tapped into the reference voltage circuit and can introduce faults that are not present in a stock vehicle.
  • The code can set even when the reference voltage is only slightly out of range, so a digital multimeter with good resolution is more reliable than a basic test light for diagnosing this circuit.

Can I keep driving with P262C?

You can usually drive the vehicle with this code, but if you notice rough running, stalling, or reduced power, keep driving to a minimum and avoid heavy loads or high speeds until the fault is repaired. Prolonged driving with a faulty reference voltage can lead to poor fuel economy and potential damage to other components that rely on the affected sensors.

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 all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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