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A relay is an electric switch that lets a small signal from the engine computer turn on the high current a radiator fan needs. When the relay fails, the fan will not run, or it will not stop. Route 66 Auto Repair in Upland tests the relay, its fuse, the wiring and the command that controls it, so a healthy fan motor is not replaced by mistake.
What are the signs of a bad fan relay?
- Fan does not come on even when the gauge reads hot
- Fan runs after the engine is off and drains the battery
- Fan works when the relay is tapped or swapped
- Fan fuse or relay socket shows heat marks
- Fan runs on only one speed
What's in the fan control circuit?
The circuit has a fuse, one or more relays, the wiring to the motor, a ground, and a controller. The controller can be the engine computer or a separate fan module that reads coolant temperature and AC pressure. Some cars use resistors or a second relay for low and high speed.
A relay failure is often a burnt contact inside, which can work one day and not the next. Heat at the socket can also damage the fuse box. For fan switch type systems, see radiator fan switch repair. For wiring beyond the fan, we use electrical system inspection.
Our fan relay repair process
Step 1: Command test
We command the fan with a scan tool and listen for the relay click.
Step 2: Circuit checks
Fuse, relay coil and contact, socket and output voltage are measured.
Step 3: Check the controller
If the relay never gets a command, we look at the sensor and control module inputs.
Step 4: Repair and verify
The relay, socket or wiring is repaired and the fan is tested hot at idle and after shutdown.
What's included in fan relay repair
Included on the work order
- 01Scan tool fan command test
- 02Fuse and relay test
- 03Relay socket and wiring inspection
- 04Fan control input check
- 05Relay, fuse or socket repair as quoted
- 06Hot idle and shutdown check
Is it a need-now or need-later repair?
Need now: call
- Fan not running when the engine is hot
- Fan running after shutdown and killing the battery
Need later: book
- Occasional relay click delay with normal temperatures
- Mild discoloration at the socket with a working fan
How pricing and timing work
A relay itself is a small part. Socket or fuse box damage costs more, and a control module more still. The diagnostic fee is stated at the counter before testing and applies to approved related repair. If the AC is also warm because the fan was off, we recheck it after the repair; if it still needs service, it gets a leak test before any recharge.
Aftercare
Listen after shutdown. A short run-on can be normal, but a fan that keeps going for a long time is not. If the battery goes flat overnight, call (909) 608-7699. Our radiator fan motor repair page covers the other side of this circuit.
Frequently asked questions
Can I swap the fan relay with another one in the fuse box?
If an identical relay is there, it is a quick home test. Only swap with the same part number, and check your manual first.
Why does my fan relay keep failing?
A fan motor drawing too much current can burn relay contacts. We test the motor too so the new relay lasts.
Is a bad relay a safety risk?
An engine can overheat in traffic without its fan, and a relay stuck on can drain the battery. Both are worth fixing soon.