A technician is diagnosing a vehicle with an intermittent no-start condition. The technician suspects a faulty ignition relay. Using a digital multimeter, the technician performs the following tests: 1) Verifies 12V at terminal 30 (power input) of the relay socket. 2) Verifies 12V at terminal 85 (coil ground control) when the key is in the 'start' position. 3) Verifies a good ground at terminal 86 (coil power input). Which of the following is the MOST appropriate next step in the diagnosis?
- AReplace the ignition relay with a known good one.
- BPerform a voltage drop test on the main power feed to terminal 30.
- CCheck for continuity between terminal 87 and the ignition system.
- DCheck for 12V at terminal 87 (output to ignition system) with the key in 'start'.
Show answer & explanationAnswer & explanation
Correct answer: A. Replace the ignition relay with a known good one.
The technician has confirmed that all necessary inputs to the relay are present: constant power (30), control power (85), and control ground (86). If these inputs are correct, the relay coil should energize, and the internal contacts should close. If the vehicle still has an intermittent no-start, the most logical next step is to suspect the relay itself and swap it with a known good one to see if the condition changes. Measuring output (A) is a good step but implies the relay is already suspected and needs to be tested for functionality first.
Why the other options are wrong
- B. Since 12V is present at terminal 30, a voltage drop test there is not the immediate next step, as power is confirmed to be reaching the relay.
- C. Continuity to the ignition system is important, but only after confirming the relay is actually outputting power.
- D. This is a good check to confirm relay output, but replacing the relay first is often quicker once all inputs are verified.
Relay Input Verification
Confirming the presence of all necessary power and ground signals at a relay's input terminals to determine if the relay itself or its control circuit is faulty.
- Requires checking constant power, switched power/ground, and constant ground.
- If inputs are good but output is missing, suspect the relay.
- Often uses a multimeter or test light.
Memory trick: Inputs Good, Relay Next: Swap it Out, See the Start.