INSTRUMENTS (Description): DESCRIPTION AND OPERATION (page 15 of 37)

INSTRUMENTS

DESCRIPTION AND OPERATION

88-19

High engine coolant temperature warning lamp

The high engine coolant temperature warning lamp within the instrument pack utilises a red LED and a clear legend. 
The ECM illuminates the LED when it detects the engine coolant has exceeded a temperature of 121 

°

C (250 

°

F) and 

switches it off when the coolant temperature drops below 118 

°

C (244 

°

F). The ECM also illuminates the high engine 

coolant temperature warning lamp when it detects the PWM duty cycle to the temperature gauge is out of range. If it 
is greater than 94% duty cycle when the engine is hot, or less than 8% duty cycle when the engine is cold, the engine 
coolant temperature gauge pointer will indicate cold, thus alerting the driver with an additional visible warning.

When the ignition is switched on, the ECM illuminates the LED to provide a self-check, providing there is no fault it 
will remain illuminated for 3 seconds or until the ignition is switched off.

The response of the engine high temperature warning lamp varies according to engine type and market, there are 
three conditions:

l

V8 - Gulf.

l

V8 - all markets except Gulf.

l

Diesel - all markets.

The vehicle configuration determines which condition is set.

The PWM duty cycle thresholds for illuminating and extinguishing the warning lamp are given in the table below. 

The power input for the LED is supplied by the instrument pack via fuse 27. The ECM controls the earth path to 
illuminate the warning lamp.

Market

Lamp on

Lamp off

V8 - Gulf

79.8 

±

 2%

77.8 

±

 2%

V8 - all markets except Gulf

77.8 

±

 2%

75.7 

±

 2%

Diesel - all markets

78.8 

±

 2%

76.8 

±

 2%