GM Service Manual Online
For 1990-2009 cars only

High Beam Telltale Indicator Lamp

The high beam telltale indicator lamp receives power from the battery, through the instrument cluster. When the headlamp switch is in the HIGH BEAM position, it supplies a ground to the DRL logic which turns the indicator ON. This indicates to the operator of the vehicle that the high beams are ON. The indicator also comes ON when the flash-to-pass feature is used.

Seat Belt Telltale

If the driver's seat belt is not buckled, the seat belt telltale will come ON and stay ON for 7 seconds. If the driver's seat belt is not buckled after 7 seconds, the lamp will remain ON for an additional 13 seconds, followed by about 100 seconds of flashing. If the driver's seat belt is buckled at any time after the initial 7 second period, the lamp will be immediately turned OFF.

Air Bag Telltale

The AIR BAG telltale indicator lamp is powered by ignition voltage and grounded by the SIR lamp driver module. The SDM controls the lamp by providing a signal to the lamp driver. The lamp driver module uses the SDM signal to determine when to provide a ground for the AIR BAG telltale. The AIR BAG telltale indicator lamp is used in the SIR system to notify the vehicle's operator of the following:

  1. Correct system operation by flashing 7 times when the ignition switch is first turned ON. The telltale will turn OFF if the system is OK.
  2. To warn the operator of the vehicle of SIR electrical system malfunctions which could potentially affect the operation of the SIR system.

The AIR BAG telltale is the key to driver notification of SIR system malfunctions.

Service (Wrench) Telltale

The SERVICE (Wrench) telltale is pulled to ground by the powertrain control module (PCM). When the lamp is pulled to ground, current from the ignition circuit flows through the indicator lamp, allowing it to come ON. The PCM will turn the SERVICE (Wrench) telltale ON for all non-emission related DTCs that require that a telltale be turned ON (some DTCs do not turn on a telltale but are stored to aid in diagnosis).

The SERVICE (Wrench) telltale will also be turned ON if the ABS control module has detected a fault in its own warning indicator system. If the ABS system cannot turn on its own telltale, a message will be sent to the PCM through the class 2 data bus (circuit 1807) to turn on the SERVICE (Wrench) telltale.

The SERVICE (Wrench) telltale will be turned ON for 2-3 seconds when the ignition is turned to RUN for a bulb test.

Malfunction Indicator Lamp (MIL) (Service Engine Soon) Telltale

The MIL (SERVICE ENGINE SOON) telltale is pulled to ground by the PCM. When the lamp is pulled to ground, current from the ignition circuit flows through the indicator lamp, allowing it to come ON. This indicates to the operator of the vehicle that there is a possible problem with the engine/transaxle control system.

The MIL will only be turned ON for emission related faults.

During engine start-up, the MIL (SERVICE ENGINE SOON) telltale is turned ON, for approximately 2-3 seconds when the ignition is turned to RUN for a bulb check.

Low Fuel Telltale

The low fuel telltale is turned to ground by the PCM. When the lamp is pulled to ground, current from the ignition circuit flows through the telltale lamp, allowing it to come ON. The PCM will turn the lamp ON when the fuel level in the tank reaches approximately 1.5 gallons.

Engine Coolant Temp/Low Coolant/Auto Trans Fluid Temp Telltale

The PCM monitors the inputs of the ECT sensor, transmission fluid temperature sensor and the coolant level switch to determine if the ECT, automatic transmission fluid temperature and coolant level are within normal operating ranges.

When either of the sensors signals a temperature that is above the specified range or the coolant level switch opens due to a low coolant level in the coolant surge tank, the PCM will ground circuit 35 and turns the engine coolant temp/low coolant/auto trans fluid temp telltale indicator lamp ON to inform the operator of the vehicle that one of the above conditions has occurred. During engine start-up the engine coolant temp/low coolant/auto trans fluid temp telltale indicator lamp is turned ON by the PCM for a bulb check.

Oil Pressure Telltale

The oil pressure telltale indicator lamp is switched to ground by the oil pressure switch. When the lamp is switched to ground, ignition voltage flows through the lamp, allowing it to come ON. This indicates to the operator of the vehicle that the oil pressure has dropped below a specified limit.

The oil pressure indicator lamp will come ON, for approximately 1-2 seconds at engine start-up, until the oil pressure raises enough to open the oil pressure switch, for a bulb check.

Change Oil Soon Telltale

The change oil soon telltale is turned ON by the cluster when it receives a command from the PCM. The change oil soon telltale is commanded ON based on a calculated value of time and mileage. This indicates to the operator of the vehicle that the oil should be changed as soon as possible.

Traction ACTIVE Telltale

The low traction active telltale indicator lamp is pulled to ground by the antilock brake system (ABS) control module and powered by ignition voltage. When the traction control system attempts to prevent wheel slip, the traction active telltale will begin to flash.

ABS Telltale

The ABS telltale is turned ON by the ABS control module. The ABS control module controls the ABS telltale indicator lamp through the telltale control logic on the I/P cluster speedometer printed circuit board. When the ABS control module grounds the input of the cluster, the transistor is OFF and the ABS telltale is OFF. If the ABS control module ungrounds the circuit, or the circuit becomes open and ignition voltage is present at the cluster, the transistor turns ON and the ABS telltale indicator comes ON.

The ABS telltale indicator lamp is turned ON, for approximately 2 seconds, during engine start-up by the ABS control module for a bulb check.

If the telltale stays ON, it informs the driver that a problem has occurred and that the ABS system has been disabled. The vehicle should be taken in for service as soon as possible.

The telltale will flash in only one case. If DTC 87 is set, and subsequently during the same ignition cycle a fault occurs such that the rear motor is not at home the telltale will flash. On subsequent ignition cycles, the ABS telltale will be on solid. When the rear motor is not at home, the car does not have rear brakes. Consequently, the ABS control module will turn on the BRAKE telltale.

For DTCs 11, 13, 75, 87 and 94, the ABS control module will not be able to turn the ABS telltale on, but will send a message to the PCM through the class 2 data bus (circuit 1807) to turn on the SERVICE (Wrench) telltale.

Brake Telltale

The brake telltale indicator lamp is switched to ground by either the low brake fluid switch (indicating low brake fluid), ABS control module (indicating a possible problem within the mechanical function of the brakes), or the park brake switch. When the BRAKE telltale indicator lamp is switched to ground, current from the ignition circuit flows through the indicator lamp, allowing it to come ON. This indicates to the operator of the vehicle that the park brake is engaged, brake fluid is low, or there is a possible problem in the mechanical portion of the ABS.

During engine start-up, the brake indicator lamp will come ON for 3 seconds by the integrated circuit built into the I/P cluster tachometer for a bulb check.

Charge (Battery) Telltale

The charge (battery) telltale is pulled to ground by the voltage regulator, located internal to the generator. When the lamp is pulled to ground, ignition voltage flows through the lamp, allowing it to come ON. This indicates to the operator of the vehicle that there is a possible problem in the charging circuit.

The charge (battery) telltale indicator lamp will turn ON, for approximately 1-2 seconds, during engine start-up until the voltage regulator senses voltage output by the generator for a bulb check.

Liftgate Ajar Telltale

The liftgate ajar telltale indicator is grounded at all times and is switch to power through the cargo lamp switch. When the liftgate has been opened, the cargo lamp switch will close providing voltage to the indicator lamp and the cargo lamp.

Daytime Running Lights (DRL) Telltale

The DRL ON telltale is controlled by the DRL logic located on the speedometer printed circuit board. The telltale will be ON whenever DRL is in operation.

The DRL ON telltale will turn OFF if the High or Low Beams headlamps are activated or if a High Beam Headlamp fails however, if both high beams fail the DRL will turn ON again. This is because the DRL circuitry is unable to identify this condition.

Important: Low resistance high beam bulbs or high charging system voltage can cause a flickering DRL telltale.

The DRL ON telltale will turn OFF if the High or Low Beams headlamps are activated or if a High Beam Headlamp fails. However, if both high beams fail, the DRL will turn ON again. This is because the DRL circuitry is unable to identify this condition.

Left Turn Signal Lamp

The left turn signal lamp is switched to power by the left turn signal switch. When the switch is in the left turn position, current flows though the indicator lamp which is connected to ground within the cluster. This indicates to the operator of the vehicle that the left turn signal is operating. If both the left and right turn signal indicator lamps are flashing, the hazard flashers are ON.

Right Turn Signal Lamp

The right turn signal lamp is switched to power by the right turn signal switch. When the switch is in the right turn position, current flows though the indicator lamp which is connected to ground within the cluster. This indicates to the operator of the vehicle that the right turn signal is operating. If both the right and left turn signal indicator lamps are flashing, the hazard flashers are ON.

Instrument Cluster Illumination Lamps

The instrument cluster has two front flood illumination lamps and four rear back-lighting lamps. The signal to control these instrument cluster illumination lamps is a pulse width modulated ground signal received from the instrument panel dimmer (circuit 44).

The duty cycle of the pulse width modulated (PWM) signal is varied by the vehicle's operator rotating the knob of the instrument panel dimmer. The duty cycle varies from approximately 20 percent LO to 100 percent HI.