How to Check for Car Relay Issues?

[Kieran]

Methods for checking car relays are as follows: 1. Inspect the operational performance of the car relay. Turn on the ignition switch, then listen with your ear or a stethoscope for any engagement sound inside the control relay, or feel for any vibration in the relay. If present, it indicates the relay is functioning normally, and the appliance's non-operation is due to other reasons; otherwise, the relay is malfunctioning. You can also remove the relay for testing. For example, if the air conditioning compressor is not working, start the engine, then turn on the blower switch and the air conditioning switch. Next, unplug the air conditioning compressor relay's connector to assess. If you can hear the relay activating, and when the relay is removed, the engine speed noticeably drops, and when the relay is reinserted, the engine speed increases, it indicates the air conditioning compressor relay and its control circuit are normal. Regarding the relay's location, any relay and fuse marked with a dashed line in the circuit schematic are generally located in the central distribution box. 2. Inspect the ECU. Poor ECU grounding may affect the relay's normal operation. With the ignition switch on, if you don't hear the fuel pump running and there's no high-voltage spark, check the ignition coil. If there's no power at the plug, but the primary and secondary resistances are normal, measure the vehicle's dual-seal injection relay. If its plug has 12V power, but replacing the dual-seal injection relay still results in no high-voltage spark or relay engagement sound, use a wire to directly ground the dual-seal injection relay's pin 10. If you hear the relay engage and the engine starts successfully, but strangely, removing this ground wire doesn't stop the engine, and after turning off the ignition switch and restarting, it operates normally. The analysis suggests that poor engine ECU grounding causes the relay coil's supply voltage to be very low (sometimes only around 2V), preventing the relay from engaging. Direct grounding provides 12V to the relay, allowing it to engage and the engine to start. After removing the temporary ground wire (with the ignition switch still on), the relay maintains a lower holding voltage (a common feature of general relays), which, even at 2V, keeps the relay engaged, so the engine doesn't stall. Turning off the ignition switch may restore normal operation due to the circuit's self-induced electromotive force being much higher than the supply voltage, potentially fixing poor grounding temporarily. However, the fault may recur, so the permanent solution is to properly address the poor grounding. 3. Reduce the contact resistance of the car relay's contacts. The contact resistance in small automotive electromagnetic relays mainly consists of constriction resistance and surface film resistance. The contact resistance depends on the contact form, material properties, and surface treatment. Therefore, to reduce the relay's contact resistance, with a given contact pressure, you can improve the contact state or upgrade the contact material.

[BradyMarie]

As an average car owner, checking automotive relays is actually not difficult. First, open the hood and locate the relay box, typically near the battery or fuse box. Then, visually inspect the relay for obvious damage such as burns, bulges, or rust. Next, perform an operational test: for example, turn on the headlights or start the engine, and listen carefully for the relay's clicking sound - if silent, it's likely faulty. If you have a multimeter handy, you can test the relay's coil resistance: place the probes on the coil terminals, with normal values ranging between 30-100 ohms; infinite or zero readings indicate failure. For more thorough contact testing, the contacts should conduct when the coil is energized. A quick fix is to directly replace it with a known-good relay of the same model - if it works, it confirms the original was defective. Notably, relay failures may cause starting issues or lighting malfunctions, especially prone during rainy/snowy weather. It's recommended to perform a quick check during annual maintenance, and don't forget to clean the connector to prevent oxidation. I once had an AC relay fail in summer - the heat was unbearable. Early detection saves trouble.

[Victor]

I enjoy working on my own car, and checking relays is quite an interesting task. I always start by disconnecting the car battery to prevent short circuits, then locate the relay. Operate the switch, like the horn button, and listen closely for a clicking sound—no sound means trouble. If you have the tools, use a multimeter to test the coil: connect it to the two small terminals, and the resistance should be within the standard range. For contact inspection, use a meter—contacts should be open when de-energized and closed when powered. During testing, you can directly apply 12V power to the coil to simulate activation. If you encounter sticking issues, disassemble it to check for carbonized contacts—cleaning might fix it. Relatedly, when upgrading car lights, choose a matching relay to avoid burnout from excessive current. I always keep a few spare relays handy for emergencies. Safety reminder: wear insulated gloves and avoid testing in damp environments. DIY like this saves money, builds knowledge, and makes the car more reliable.

[Kirsten]

With years of driving experience, I've gained expertise in checking relays. Here's how: First, inspect the appearance for any burn marks or deformities. Second, listen for a clicking sound during startup operation—if present, it's normal. Third, perform a simple test: use a multimeter to measure the coil resistance; replace if the value is incorrect. Fourth, swap test: try replacing it with a known good relay. Locating the correct position is crucial, as relays for different functions are placed differently. Relatedly, relays in older cars are prone to aging and failure, leading to hard starts or headlight malfunctions. It's recommended to clean the connector ports every six months to prevent dust buildup. I often encounter cold start issues in winter, which turned out to be frozen relays—warming them up solves the problem. Early detection can reduce the risk of breakdowns.