DTC 21

Fig. 020 - WIRING DIAGRAM for Code 21 Metering Valve Sensor (Signal Voltage Low). VIN N, VIN T:

CODE 21

METERING VALVE SENSOR

(SIGNAL VOLTAGE LOW)

4.3L VIN "T"

5.7L VIN "N"

Code 21 means that the ECM has seen the following:
a. Low voltage at ECM terminal "R".
b. Or grounded MVS signal circuit.
c. For a time in excess of 10 seconds.

Fig. 019 - Chart For Code 21 Metering Valve Sensor (Signal Voltage Low).:

1. Checks for V-ref at MVS harness connector. Normal reading should be about 5 volts. (4 Volts or above)
2. Determines if low voltage noted in step #1 was due to open in sensor return or low 5 V-ref. supply at MVS Terminal "D".
3. Checks to see if low V-ref voltage at MVS 'Terminal "D" is due to a grounded wire pulling V-ref low or an open circuit, including the ECM.
4. Separates an electrical circuit problem from a faulty MVS. If the circuit is OK, normal voltage reading will be above 4 volts.