Circuit Operation - Gauges and Warning Indicators

ABS WARNING INDICATOR
The Antilock Brake System (ABS) Warning Indicator is controlled by the Electronic Brake Control Module (EBCM). The EBCM will turn the Indicator "ON" for approximately 3 seconds during Engine start up for a bulb check. The EBCM will flash the ABS Warning Indicator to warn the driver that an ABS malfunction exists which may have degraded base brake performance. A solid (not flashing) ABS Warning Indicator warns the driver that a problem has been detected that affects the operation of ABS (ABS may be disabled), but normal brake performance will remain. For more information on ABS, refer to Antilock Brake System. Antilock Brakes / Traction Control Systems

"AIR BAG" WARNING INDICATOR
The "AIR BAG" Warning Indicator is controlled by the Inflatable Restraint Diagnostic Energy Reserve Module with Sensor (SDM). The SDM will turn the Indicator "ON" for approximately 3 seconds during engine start up for a bulb check. The SDM will turn the Indicator "ON" to warn the driver of a Supplemental Inflatable Restraint (SIR) Electrical System malfunction, which could potentially affect the operation of the SIR System. For more information on SIR, refer to Supplemental Inflatable Restraint. Air Bag Systems

"BRAKE" WARNING INDICATOR
The "BRAKE" Warning Indicator will be illuminated when low brake fluid level in the master cylinder is sensed, the Parking Brake Switch is closed, or under control of the EBCM when certain ABS Diagnostic Trouble Codes (DTC's) are set. This Indicator is to warn the driver that a base brake problem may exist. For more information on ABS, refer to Antilock Brake System. Antilock Brakes / Traction Control Systems

ENGINE COOLANT TEMPERATURE GAGE
The Engine Coolant Temperature Gage is operated by two coils. Battery voltage is applied to both coils. One is grounded directly, and the other is grounded through the Engine Coolant Temperature Sender. The Engine Coolant Temperature Sender has 44 ohms resistance at 26O°F (125°C) and its resistance increases at lower temperatures. Resistance is approximately 1365 ohms at 100°F (37°C), this causes the current through the Engine Coolant Temperature Sender and one coil to increase as the coolant temperature decreases and moves the pointer.

FUEL GAGE
The pointer of the Fuel Gage is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the "E" coil and the circuit divides at the opposite end of this coil. One path continues to ground through the "F" coil. Another goes to ground through the variable resistor of the Fuel Level Sender.

When the tank is low, the resistance of the Fuel Level Sender is low. A large flow of current passes through the "E" coil and the Fuel Level Sender Resistor. This pulls the pointer towards "E" on the scale. When the tank is full, the Fuel Level Sender Resistance is high. More current now flows through the "F" coil, moving the pointer to "F" on the scale.

With two coils operating the pointer, the Fuel Gage is not affected by changes in the voltage of the system.

COOLANT WARNING INDICATOR
The Coolant Warning Indicator Control monitors the Engine Coolant Temperature Signal from the Engine Coolant Temperature Sensor. At an Engine Coolant Temperature of approximately 255°F (124°C) or a sender resistance of approximately 53 ohms, the indicator Control will illuminate the Coolant Warning Indicator. The Indicator will also illuminate for a bulb check when the Ignition Switch is in "RUN" with the Engine not running.

"LOW COOLANT" INDICATOR
The "LOW COOLANT" Indicator receives battery voltage with the Ignition Switch in "RUN," "BULB TEST" or "START" The Instrument Cluster will turn the Indicator "ON" for approximately 1 second during Engine start up for a bulb check. The Indicator is grounded by the Engine Coolant Level Switch with the coolant level in the Coolant Reservoir below minimum recommended level.

"LOW OIL" INDICATOR
The "LOW OIL" Indicator is controlled by the Powertrain Control Module (PCM). The PCM will sample the oil level once per Ignition cycle, at power-up only, if criteria has been met indicating that the oil has had sufficient time to drain into the oil pan from the last power-down. 3 minutes must elapse after power-down, if Engine coolant temperature is greater than 75°C (167°F) at power-down, for the PCM to sample oil level. If the Engine coolant temperature is less than 75°C (167°F) at power-down, the PCM looks for at least an 11°C (20°F) drop in Engine coolant temperature before sampling oil level at power-up.

LOW TRAC INDICATOR
The "LOW TRAC" Indicator is controlled by the EBCM. The EBCM will turn the Indicator "ON" for approximately 3 seconds during Engine start-up for a bulb check. The EBCM monitors the Wheel Speed Sensors for a brake lock-up (skid condition). If EBCM detects a skid condition, it will engage the ABS and turn "ON" the "LOW TRAC" Indicator. For more information on ABS, refer to Antilock Brake System. Antilock Brakes / Traction Control Systems

OIL PRESSURE WARNING INDICATOR
The Oil Pressure Warning Indicator receives battery voltage with the Ignition Switch in "RUN," "BULB TEST" or "START." The Instrument Cluster will turn the Indicator "ON" during Engine start up for a bulb check. The Indicator is grounded by the Fuel Pump/Oil Pressure Switch with low oil pressure condition.

"SECURITY" INDICATOR
The "SECURITY" Indicator is controlled by the Theft Deterrent Module. The Theft Deterrent Module will turn the Indicator "ON" for approximately 5 seconds during Engine start-up for a bulb check. If the Theft Deterrent Module detects a fault in CKT 1073, CKT 1074 or a defective Ignition key, the "SECURITY" Indicator will flash. A solid (not flashing) "SECURITY" Indicator is illuminated if the Theft Deterrent Module enters shut down mode thus preventing the vehicle from starting. For more information on Theft Deterrent System, refer to Antitheft and Alarm Systems. Antitheft and Alarm Systems

SPEEDOMETER AND ODOMETER
The Vehicle Speed Sensor (VSS) is a gear driven Permanent Magnet Generator housed in the vehicle's Transaxle. This sensor generates a sine wave output with a frequency proportional to vehicle speed. The (PCM) converts this signal to an output that is switched to ground at a frequency of 4000 pulses per mile. This signal (CKT 389) drives the Speedometer and Odometer and is used by various other components. For more information on VSS, refer to Vehicle Speed Sensor. Vehicle Speed Sensor

TACHOMETER
The Tachometer displays Engine speed in rpm. Voltage pulses are taken from the Ignition Control Module and sent to the Tachometer. It responds to the frequency of the voltage pulses which increase with Engine speed. Solid state circuits process these pulses into a signal that drives the pointer of the Tachometer.

"VOLTS" WARNING INDICATOR (CHEVROLET)
The "VOLTS," Warning Indicator is controlled by the Generator's Digital Regulator. The Instrument Cluster will turn the Indicator "ON" during Engine start-up for a bulb check. The Digital Regulator will turn the Indicator "ON" whenever it detects an undervoltage (11.2 volts) or overvoltage (16.5 volts) condition.