For 1990-2009 cars

### Circuit Description

The 5-volt reference circuit provides a signal voltage to the linear exhaust gas recirculation (EGR), manifold absolute pressure (MAP) and throttle position (TP) sensors. The return line is grounded through the powertrain control module (PCM). DTC P1635 detects a short to ground in any of the three 5-volt reference circuits inside the PCM.

### Conditions for Setting the DTC

DTC P1635 will set if the 5-volt reference signal is below 3.5 volts or above 5.5 volts. This voltage is monitored internally by the PCM.

Important: The 5-volt reference is monitored whenever the ignition is ON.

### Diagnostic Aids

When attempting to diagnose an intermittent problem use the scan tool to review the malfunction history diagnostic information. The supplemental data can be used to duplicate a problem.

Intermittents or opens suspected to be at the connector can be detected by using a diagnostic service probe. Voltage can be read on wires without disconnecting any connectors.

Check the tightness of the female terminal grip with a spare male terminal.

If DTCs P0563, P0108, P1106, P1122 or P0122 set a short to B+ on the 5-volt reference circuit is probable. If the short exists while attempting to diagnose, PDT communications will be lost and driveability conditions will exist.