Rick's Free Auto Repair Advice

Silverado P0480

Diagnose and fix Silverado P0480 trouble code and overheating

Shops are reporting multiple instances of a Silverado P0480 trouble code with an overheating condition. These trucks have two radiator fans and three relays. The three relays allow the fans to run at two speeds. So don’t get fooled into thinking that because the fans are running, they’re not the problem. They could be running on low speed and not pulling in enough air to cool.

Here’s how GM 2-speed radiator fans work

Low speed fan operation
The PCM provides ground to low speed fan relay control coil. The energized coil pulls the contacts closed, sending battery power to the left radiator fan motor. The left fan motor seeks ground though the s/p relay contacts and then flows through right motor to ground. This is a SERIES circuit so voltage is cut in half and both fans run at low speed.

Low speed fan operation

radiator fan wiring diagram





High speed fan operation

radiator fan wiring diagram





How to diagnose the problem

The PCM monitors input from the engine coolant temperature sensor to determine when to switch between low and high speeds. However, since the switching is accomplished by providing ground to the relays’ control coil circuit, always check for proper ground power operation at the relays. Also, check the three fuses and the relay operation. If you don’t see ground at the relays according the speed cycle, check for corrosion at the PCM connectors. That’s where shops are finding the problem. Power down the vehicle before unplugging the PCM connectors. Then remove and check for corrosion.

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Posted on by Rick Muscoplat

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