P0653 indicates the PCM has detected an abnormally high voltage on its 5-volt reference circuit B, which supplies a regulated reference voltage to one or more engine sensors. When this circuit is shorted to a higher voltage source or a connected sensor fails internally, the reference voltage rises above the expected range and the PCM sets this code.
A chafed, pinched, or corroded wire on the 5V reference B circuit can short to battery voltage or another power feed, pulling the reference line above its normal 5-volt level. This is the most common cause.
A sensor powered by the reference B circuit may fail internally and back-feed voltage onto the reference line. Disconnecting sensors on the circuit one at a time can identify the culprit.
Corroded pins, bent terminals, or water intrusion in connectors along the reference B circuit can create unwanted voltage paths and cause the PCM to detect an out-of-range reference voltage.
In rare cases the PCM's internal 5-volt reference regulator for circuit B may fail and output excessive voltage. This should only be considered after all wiring and sensors are verified good.
It depends on symptoms. If the engine runs poorly, stalls, or enters limp mode, driving risks further damage and should be avoided. If there are no drivability issues, short trips may be possible but the code should be diagnosed promptly.
No. The PCM is the least likely cause. In most cases the problem is a wiring short to voltage or a failed sensor back-feeding the reference circuit. Replacing the PCM without verifying all wiring and sensors is a common and costly mistake.
You will need a vehicle-specific wiring diagram. Reference circuit B typically feeds a defined subset of sensors, and which sensors are on it varies by make, model, and year.
Yes. If a sensor on the reference B circuit fails internally and shorts reference voltage to another voltage source, it can pull the entire reference B line high and trigger this code, even if other sensors on the same circuit are fine.