For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC C0785 00: One Undetermined Low Tire Pressure Sensor Malfunction
DTC C0785 03: One Undetermined Low Tire Pressure Sensor Battery Low
DTC C0786 00: Two Undetermined Low Tire Pressure Sensors Malfunction
DTC C0786 03: Two Undetermined Low Tire Pressure Sensors Battery Low
DTC C0787 00: Three Undetermined Low Tire Pressure Sensors Malfunction
DTC C0787 03: Three Undetermined Low Tire Pressure Sensors Battery Low
DTC C0788 00: Four Undetermined Low Tire Pressure Sensors Malfunction
DTC C0788 03: Four Undetermined Low Tire Pressure Sensors Battery Low

### Circuit/System Description

The tire pressure monitor (TPM) system has a radio frequency (RF) transmitting pressure sensor in each wheel/tire assembly. As vehicle speed increases, centrifugal force closes the sensor internal roll switch which puts the sensor into rolling mode. The sensor signals are received by the tire pressure indicator receiver. The tire pressure indicator receiver translates the data contained in the tire pressure sensor RF transmissions into sensor mode, tire pressure, and tire temperature. Once vehicle speed is 32 km/h (20 mph) or greater, the tire pressure indicator receiver waits for the sensors to go into rolling mode. If one or more sensors do not go into rolling mode, if the internal battery is low, or if the sensor does not transmit at all, the tire pressure indicator receiver will set DTC C0785, C0786, C0787, or C0788 respectively.

### Conditions for Running the DTC

Vehicle speed is 32 km/h (20 mph)or greater for 10 minutes.

### Conditions for Setting the DTC

• | A sensor does not transmit for 10 minutes.

• | A sensor internal battery voltage is low.

• | A malfunctioning tire pressure monitor receiver.

### Action Taken When the DTC Sets

The tire pressure monitor indicator icon on the instrument panel cluster (IPC) flashes for 1 minute and then remains illuminated after the ignition switch is cycled ON and the IPC bulb check is complete.

### Conditions for Clearing the DTC

• | A current DTC will clear when the malfunction is no longer present and 1 ignition cycle occurs.

• | The tire pressure indicator receiver automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

### Diagnostic Aids

• | Some aftermarket wheel valve stem holes are located further from the wheel rim than original equipment wheels. When using the TPM special tool to activate a sensor, ensure the tool antenna is no further than 15 cm (6 in) from the sensor and is aiming upward.

• | Aftermarket wheel valve stem locations can cause a sensor to not function correctly.

• | A sensor may have been damaged due to a previous wheel/tire service or flat tire event.

• | The use of other than GM approved tire sealants can obstruct the sensor pressure sensing port and cause inaccurate tire pressure readings. If this condition is verified, remove the sealer from the tire and replace the sensor. Refer to Tire Pressure Indicator Sensor Replacement.

• | Occasionally sensor transmissions are not received by the tire pressure indicator receiver due to vehicle level RF interference from items such as but not limited to aftermarket ignition systems, DVD players, CB radios, or metallic type window tinting.

• | The sensor activation procedure may have to be repeated up to 3 times before determining a sensor is malfunctioning. In the event a particular sensor's information is displayed on the special tool upon activation but the information is not displayed on the scan tool, it may be necessary to rotate the wheel valve stem to a different position due to the RF signal is being blocked by another component.

• | Occasionally, stray sensor transmissions can be received from other vehicles.

• | A sensor low battery condition will set a sensor DTC. The sensor battery status can be verified in the scan tool TPMS data list. If a sensor low battery condition is indicated on the scan tool, the sensor will need to be replaced. Refer to Tire Pressure Indicator Sensor Replacement.

### Reference Information

#### Schematic Reference

Tire Pressure Monitoring System Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Tire Pressure Monitor Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for Scan Tool Information

#### Special Tools

J-46079 Tire Pressure Monitor Diagnostic Tool

### Circuit/System Verification

1. Using the J-46079 , activate each tire pressure sensor and record the sensor transmission data for each tire location. Verify J-46079 displays the 8-digit ID number, accurate tire pressure ±27.6 kPa (4 psi), and at least a 1/4 graph signal strength displayed.

⇒ | If any of the parameters listed above are not displayed, replace the appropriate tire pressure sensor and perform the Tire Pressure Sensor Learn procedure.

2. Perform the Tire Pressure Sensor Learn procedure. With a scan tool, verify that the TP Sensors data parameters display the following:

• | ID number recorded for each sensor

• | Valid ID Status for each sensor

• | Accurate tire pressure ± 27.6 kPa (4 psi) for each tire

• | Normal Battery status for each sensor

⇒ | If any of the parameters are not as specified, replace the appropriate tire pressure sensor and perform the Tire Pressure Sensor Learn procedure.

3. Perform the Reset ECU and replace the tire pressure indicator receiver.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tire Pressure Indicator Sensor Replacement

• | Tire Pressure Sensor Learn

• | Control Module References for tire pressure indicator receiver replacement, setup, and programming