Chevrolet Silverado / GMC Sierra. Service manual — part 1606

Fig. 2: Engine Cooling Schematic - Diesel
Courtesy of GENERAL MOTORS CORP.

DIAGNOSTIC INFORMATION AND PROCEDURES

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

DTC P0480 OR P0481

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

DTC

Description

DTC P0480 or P0481

P0480: Cooling Fan Relay 1 Control Circuit
P0481: Cooling Fan Relay 2 Control Circuit

DTC P1258

P1258: Engine Coolant Over temperature - Protection Mode

Active

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptor

DTC P0480

Cooling Fan Relay 1 Control Circuit

DTC P0481

Cooling Fan Relay 2 Control Circuit

Diagnostic Fault Information

Circuit/System Description

The engine control module (ECM) commands the fans ON in either high speed or low speed,
depending on cooling requirements. In low speed, the fans are configured in series. In high speed,
the fans are configured in parallel.

In low speed operation, the ECM applies ground to the coil side of the fan low relay. Voltage is
applied directly to the left cooling fan through the switch side of the fan low relay, which is fed
by the fan 1 fuse. The right fan is connected in series to the left fan through the de-energized fan
control relay so that both operate at low speed.

In high speed operation, the ECM applies a ground to the coil side of the fan low relay, the fan
control relay, and the fan high relay. Voltage is applied directly to the right cooling fan through
the switch side of the relay, which is fed by the fan 2 fuse. The left cooling fan obtains voltage
through the fan low relay and ground through the fan control relay.

The ECM monitors the low and high speed cooling fan relay control circuits for the following
conditions:

Short to ground

Circuit

Short to

Ground

High

Resistance

Open

Short to

Voltage

Low Speed Cooling Fan Relay
Control Circuit

P0480

P0480

P0480

P0480

High Speed Cooling Fan Relay
Control Circuit

P0481

P0481

P0481

P0481

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Short to voltage

An open circuit

If the ECM detects an improper voltage level on the low or high speed ECM driver circuits, then
DTC P0480 or P0481 will set and the affected ECM driver will be disabled.

Conditions for Running the DTC

The battery voltage is between 9-18 volts.

The engine speed is greater than 400 RPM.

Conditions for Setting the DTC

The commanded state of the output driver module (ODM) and the actual state of the control
circuit do not match.

The condition is present for more than 5 seconds.

Action Taken When the DTC Sets

DTCs P0480 and P0481 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0480 and P0481 are Type B DTCs.

Diagnostic Aids

This test procedure requires that the vehicle battery has passed a load test and is completely
charged. Refer to Battery Inspection/Test .

When disconnecting electrical connectors or removing fuses and relays from a fuse block,
always inspect the component electrical terminals for corrosion and the mating electrical
terminals for tightness.

Use the J 35616 for any test that requires probing the underhood fuse block terminals,
component wire harness terminals, or the ECM wire harness connector terminals.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Component Connector End Views

Electrical Center Identification Views

Description and Operation

Cooling Fan Description and Operation (w/o LFA)

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References

Special Tools Required

J 43244 Relay Puller Pliers

J 35616 GM Approved Terminal Test Kit

Circuit/System Verification

1. Ignition ON, command the cooling fan relay 1 ON and OFF several times using the scan

tool output control function. You should hear both fans turn ON and OFF. Both should run
on low speed when turned ON.

2. Ignition ON, command the cooling fan relays 2 and 3 ON and OFF several times using the

scan tool output control function. When turned ON, the right fan should run on high and the
left fan should remain OFF.

3. Ignition ON, command the cooling fan relays 1, 2, and 3 ON and OFF several times using

the scan tool output control function. When turned ON, both fans should run on high speed.

Circuit/System Testing

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Cooling - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado