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by Bob O’Neill and Bob Lincoln
For 1984 models only, code 42 indicates that the injector control circuit 1 is open or shorted.
For 1985 and later models, code 42 indicates that the ASD (Automatic Shut Down) relay circuit is open or shorted. When code 42 is triggered the power limited light will not be lit and the system will not enter limp mode.
Poor wiring or connection - Read the page ‘How to troubleshoot drivability issues’. Check the wiring and connections from the logic module to the power module. Clean and re-grease the connectors with dielectric grease. Check the wiring and connections to injectors 1 and 2 in the injector harness (above the fuel rail) and between the harness and the power module (or SMEC) and the injector control lines between the logic module and power module.
Defective injector driver transistor - The injector signals coming from the power module (or SMEC) are driven by a Darlington transistor. A rise if about 12 volts DC occurs when the injector is off and it will drop to near zero when the injector is on. If you don’t measure this when testing the transistor, replace the power module. This test can be done by measuring the output at the connector to/from the power module piercing the insulation of the wire which feeds the injector circuit.
Poor wiring or connection – See above.
Blown fusible link to power module (or SMEC) – A good fusible link will look like a large round rubber band. A blown fusible link will change color and bulge when it blows. If a white fusible link is located and is gray in color around the area which has blown. The link which powers the ASD relay is the one on the two link circuit. Don’t confuse this with the four or five link circuit. The link supplies power to the ASD relay as well as the voltage sense circuit for the logic module. If the link has failed, code 42 may also be accompanied by a code 16.
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