Code 21: Tune Select Resistor Fault

To suit individual market requirements, a tune select resistor is connected across terminals No. 5 and 27 of Engine Control Module (ECM). Tune select resistor is located adjacent to ECM, and strapped to CHECK ENGINE cable assembly. Value of resistor is dependent on market application. For USA models, resistor (with White wire) value is 3900 ohms. Code 21 identifies that the tune select resistor is open circuit. To test tune select resistor, perform Test "A". See Fig 1 . After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Fig 1: Tune Select Resistor Fault Test "A"

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