What Does P0699 Mean?
The PCM has detected that the 5-volt sensor reference voltage bus "C" is reading higher than the expected 5V level. This condition is unusual and typically indicates a short to a higher voltage source in the reference circuit, or an internal PCM regulator malfunction producing overvoltage. All sensors on the "C" reference bus will report falsely high readings, leading to incorrect air/fuel ratios, timing errors, and overall poor driveability.
Safety Warning
Overvoltage on the sensor reference bus causes the PCM to receive falsely elevated sensor readings, which can result in severe fuel trim errors, potential engine damage from lean conditions, and unpredictable driveability. Do not drive until repaired.
Common Causes
35%
Short to battery or ignition voltage in the 5V reference "C" wiring harness
25%
Internal PCM 5V reference "C" regulator failure producing overvoltage
20%
Pinched or chafed wiring where the 5V reference wire contacts a power supply wire
10%
Contaminated or water-damaged connector creating unintended voltage path
10%
Aftermarket wiring modifications incorrectly tapped into the sensor reference circuit
Diagnostic Steps
1
Measure the 5V reference "C" voltage at the PCM connector pin; if the PCM itself is outputting above 5.2V, the internal regulator has failed and PCM replacement is indicated.
2
If PCM output is correct (4.9-5.1V), disconnect sensors one at a time while monitoring the reference voltage at the PCM; look for a sensor or circuit introducing external voltage.
3
With all sensors disconnected, measure voltage on the 5V reference wire; any voltage above 0.5V with sensors disconnected indicates a short to a power source in the harness.
4
Trace the 5V reference "C" harness looking for areas where it runs alongside power wires (injectors, ignition coils, alternator); inspect for insulation damage or pinched wires.
5
Check for any aftermarket installations (remote starters, alarm systems, performance tuners) that may have spliced into the sensor reference circuit.
Estimated Repair Cost
$100 - $700
Parts + labor, varies by vehicle and location
The PCM has detected that the 5-volt sensor reference voltage bus "C" is reading higher than the expected 5V level. This condition is unusual and typically indicates a short to a higher voltage source in the reference circuit, or an internal PCM regulator malfunction producing overvoltage. All senso...
The most common cause of P0699 (Sensor Reference Voltage "C" Circuit High) is: Short to battery or ignition voltage in the 5V reference "C" wiring harness
Typical repair costs for P0699 range from $100 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Overvoltage on the sensor reference bus causes the PCM to receive falsely elevated sensor readings, which can result in severe fuel trim errors, potential engine damage from lean conditions, and unpredictable driveability. Do not drive until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0699 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Electrical / Sensor Reference
Difficulty
Type
Generic (SAE)
Recommended Tools
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