Check Gauges Lamp: Description and Operation

A check gauges indicator is standard equipment on all instrument clusters. The check gauges indicator is located on the left side of the instrument cluster, to the left of the voltage gauge.

The check gauges indicator consists of a stencil-like cutout of the words CHECK GAGES in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A red Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in red through the translucent outer layer of the overlay when it is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The check gauges indicator is serviced as a unit with the instrument cluster.

The check gauges indicator gives an indication to the vehicle operator when certain instrument cluster gauge readings reflect a condition requiring immediate attention. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) on vehicles equipped with a gasoline engine, or from the Engine Control Module (ECM) on vehicles equipped with a diesel engine over the Controller Area Network (CAN) data bus.

The check gauges indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED will always be off when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the check gauges indicator for the following reasons:
- Bulb Test - Each time the ignition switch is turned to the ON position the check gauges indicator is illuminated for about two seconds as a bulb test.
- Engine Temperature High Message - Each time the cluster receives three consecutive bus messages from the PCM or ECM indicating the engine coolant temperature is high, the check gauges indicator will be illuminated and a single chime is sounded. The indicator remains illuminated until the cluster receives a message from the PCM or ECM indicating that the engine coolant temperature is not high, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Engine Oil Pressure Low Message - Each time the cluster receives three consecutive bus messages from the PCM or ECM indicating the engine oil pressure is low, the check gauges indicator will be illuminated and a single chime is sounded. The indicator remains illuminated until the cluster receives a message from the PCM or ECM indicating that the engine oil pressure is not low, or until the ignition switch is turned to the OFF position, whichever occurs first. The cluster will only turn the indicator on in response to an engine oil pressure low message if the engine speed is greater than zero.
- System Voltage Low (Charge Fail) Message - Each time the cluster receives three consecutive messages from the PCM or ECM indicating the electrical system voltage is low (charge fail condition) or that the battery temperature sensor input is an open circuit, the check gauges indicator will be illuminated and a single chime is sounded. The indicator remains illuminated until the cluster receives a single message from the PCM or ECM indicating the electrical system voltage is not low, or until the ignition switch is turned to the OFF position, whichever occurs first.
- System Voltage High Message - Each time the cluster receives three consecutive messages from the PCM or ECM indicating the electrical system voltage is high, the check gauges indicator will be illuminated and a single chime is sounded. The indicator remains illuminated until the cluster receives a single message from the PCM or ECM indicating the electrical system voltage is not high, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Actuator Test - Each time the cluster is put through the actuator test, the check gauges indicator will be turned on, then off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.

On vehicles with a gasoline engine, the PCM continually monitors the engine temperature, oil pressure, and electrical system voltage, then sends the proper messages to the instrument cluster. On vehicles with a diesel engine, the ECM continually monitors the engine temperature, oil pressure, and electrical system voltage, then sends the proper messages to the instrument cluster. For further diagnosis of the check gauges indicator or the instrument cluster circuitry that controls the LED, refer to testing.

For proper diagnosis of the PCM, the ECM, the CAN data bus, or the electronic message inputs to the instrument cluster that control the check gauges indicator, a diagnostic scan tool is required.