15 COOLANT SENS

VOLTAGE LOW

When this problem has been corrected (perhaps by replacing the sensor) the stored fault code (15) must be removed from the ECM, otherwise the ECM will still think something is wrong. This is what the CLEAR CODES function is for. After clearing codes, the engine should be started and a final check for any stored fault codes made, just to be certain that nothing else has occurred.

The ACTUATOR TEST feature is a method of testing the ECM outputs when the engine is turned off. For example to test the injectors involves sending a signal from the code reader to trigger a special program in the ECM that, in turn, causes the injectors to open and close every second. The injectors can be heard quite clearly 'ticking' like a clock every second. With this we have clear proof that a signal is able to reach the injectors, we DO NOT KNOW if the injectors are blocked or gummed, so we do not know if any fuel can get into the engine...there are other ways of testing for that.

The final group of tests are COMPONENTS, (this is another way of saying sensors) where we can show the voltage, time or angle of various sensors that provide input to the ECM.

Remember two important things ... one ... the ECM can only measure what is happening to the car using the sensors it is connected to. If there is no sensor it cannot be measured. This may seem obvious but some people seem to think computers are all-powerful.

And two, the ECM calculates the value that we display, the code reader is NOT connected directly to the sensor. The display you see is what the ECM "thinks" is the correct value. So when you see Coolant Temperature 79^oC and the engine is stone-cold you know something is wrong, but the ECM doesn't. This is a vital point to understand about code-readers that connect to the diagnostic socket; they can only display what the ECM is programmed to show and what the ECM calculates from its inputs.

Steve Davies

February 1997