Code 21, Metering Valve Sensor (MVS)
Code 21 indicates ECM has read either low voltage at ECM terminal "R" grounded MVS signal circuit for a time in excess of 10 seconds.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- Checks for reference voltage at MVS harness connector. Normal reading should be 4 volts or above.
- Determines if low voltage in step 1) was due to open in sensor return or low 5 volt reference voltage supply at MVS terminal "D".
- Checks if low reference voltage at MVS terminal "D" is due to grounded wire pulling reference voltage low or open circuit (including ECM).
- Separates an electrical circuit problem from a faulty MVS. If the circuit is good, normal voltage reading will be above 4 volts.