P0699: Sensor Reference Voltage Circuit High
The P0699 code indicates that the Engine Control Module (ECM) has detected a voltage higher than the specified range on the 5-volt reference circuit that powers various sensors (e.g., throttle position, manifold absolute pressure, fuel tank pressure). This circuit is critical for sensor operation; a high voltage condition can cause erratic sensor readings, leading to drivability issues. Common causes include a short to voltage in the wiring, a faulty sensor, or a malfunctioning ECM.
1. Most Common Causes
- Short to battery voltage (B+) in the 5V reference 'C' circuit
- Faulty sensor (MAP, TPS, APP, fuel rail pressure, etc.) backfeeding voltage into the reference circuit
- Damaged wiring, corroded connectors, or loose terminals in the reference 'C' circuit
- Internal PCM failure (damaged reference voltage driver)
- Internal short circuit in a sensor sharing the reference 'C' bus
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor engine performance (hesitation, stalling, rough idle)
- Erratic sensor readings (e.g., throttle position, fuel pressure)
- Possible no-start condition
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all codes and freeze frame data.
Step 2: Visually inspect the 5V reference circuit wiring and connectors for damage, corrosion, or shorts.
Step 3: Disconnect sensors one by one while monitoring the 5V reference voltage with a multimeter; if voltage drops to normal (5V), the last disconnected sensor is likely faulty.
Step 4: Check for shorts to battery voltage or ground in the circuit using a multimeter.
Step 5: If all sensors and wiring are good, test the ECM output; if voltage is still high, replace the ECM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can cause unpredictable engine behavior, stalling, or no-start conditions, which may be dangerous.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, depending on the cause. Sensor replacement is usually $50-$100, while ECM replacement can be $200-$500.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.