For 1990-2009 cars

### Circuit Description

One of the three PCM 5 volt reference circuits provide reference voltage to the A/C pressure sensor, fuel tank pressure sensor and throttle position (TP) sensor. The current for each 5 volt reference circuit flows through the sensor to ground, which is provided internal to the PCM. The PCM regulates the 5 volts reference voltage to 5 volts under most normal operating conditions. this is necessary for accurate sensor information.

### Diagnostic Aids

To locate an intermittent problem, use a scan tool to monitor any of the sensors tied to the 5 volt reference circuit (A/C pressure sensor, fuel tank pressure sensor and TP sensor). Wiggling the wires while watching for a change in any one of the sensors may locate the area where a short to ground or a short to voltage on the 5 volt reference circuit could lie.

If all three sensors tied to the 5 volt reference circuit set low sensor voltage DTCs, a short to ground probably exists on the 5 volt reference circuit.

If DTC P0453 and P0105 are set, a short to voltage on the 5 volt reference circuit may exist. If a short to voltage occurs on the 5 volt reference circuit.

If DTC P0453 and P0105 are set, a short to voltage on the 5 volt reference circuit may exist. If a short to voltage occurs on the 5 volt reference circuit, the scan tool will display TP ANGLE between 20 and 30% with the throttle plate closed, A/C HIGH SIDE PRESSURE will read over 2.40 volts with A/C Off and the FUEL TANK PRESSURE will read over 4.00 volts.

Driveability conditions will exist if a short on the 5 volt reference circuit is present.

The MAP sensor circuit contains on it's own 5 volt reference supply. The ECT and IAT circuits are on their own 5 volt reference supply as well.

Important: Inaccurate readings will occur if resistance measurements are taken on the A/C pressure sensor or fuel tank pressure sensor. These sensors contain an internal amplifier circuit that requires applied voltage to function properly.