Q: How to test and diagnos a defective relay on Chevrolet Cobalt,HHR and Saturn ION?
A: Several electrical accessories in a vehicle, such as the fuel injection system, Horns, starter, and fog lamps, use relays to transmit the electrical signal to the component. Relays have a control circuit and a power circuit, and if a relay is defective, the corresponding component will not operate properly. Most relays are located in the engine compartment fuse/relay box, with some specialized relays found above the interior fuse box in the console. To test a relay, it can be removed and checked for continuity using an ohmmeter. The terminals of ISO relays, commonly used in these vehicles, are numbered to indicate their circuit connections and functions. Terminal 85 and 86 are typically the control circuit, with terminal 30 connected to the battery voltage source and terminal 87 connected to the component being powered. If the relay contains a diode or resistor, specific polarity and resistance values should be observed. If the relay fails any of the tests, it should be replaced.