Secondary Air Injection System Diagnosis. GMC Truck GMC K Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2000 🢒 GMC K Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Secondary Air Injection System Diagnosis

VCM Connector End Views
Engine Controls Components
A.I.R., IAC, and MAF Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

A fused ignition voltage is supplied to the AIR pump relay. The VCM controls the AIR pump by grounding the AIR pump relay control circuit. This energizes the relay and supplies voltage to the AIR pump clutch. When the fuel system goes into closed loop, the VCM opens the ground to the AIR pump relay control circuit.

Diagnostic Aids

An AIR pump that is stuck on could cause a fuel trim lean code.

The AIR shut off valve is spring loaded and requires air pressure to open for air to flow. A leak in the hose between the AIR pump and the AIR shut off valve could cause a no flow condition even though the pump is flowing air.

A weak or worn AIR pump might flow air but may not be able to overcome the spring in the AIR shut off valve.

An AIR supply hose that is melted before the check valve could indicate exhaust gas back-flow past the check valve.

Low AIR system volume may cause a DTC P1415, P1416 or an intermittent complaint.

Inspect for the following conditions:

•	Pinched, kinked or restricted AIR pipes, hoses or fittings

•	Leaks, holes, loose fittings or hoses

•	Restricted or obstructed AIR pump inlet hose

•	Worn or loose AIR pump drive belt

Air flowing to the exhaust ports at the wrong time can cause a false lean HO2S indication and cause the VCM to add extra fuel. This will result in increased catalytic converter temperature, because more fuel and air will be oxidizing in the converter.

The AIR system is not completely noiseless. Under normal conditions noises rises in pitch as engine speed increases.

If excessive noise is caused by the AIR system, check for the following:

•	A seized AIR pump

•	Proper mounting and bolt torque of the pump

•	Proper routing and connections of the hoses

An intermittent may be caused by any of the following conditions:

•	A poor connection

•	Rubbed through wire insulation

•	A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to step numbers on the diagnostic table.

This step will determine if the AIR system is functioning correctly.

This step will ensure that the VCM is capable of turning the AIR pump OFF.

This step will determine if the VCM is capable of controlling the AIR pump relay.

This step is to check for a short to voltage on the control circuit.

This step will determine if the pump is capable of flowing air.

This step is to check for a weak or worn AIR pump. If the pump is weak it could flow air but may not be able to overcome the shut off valve.

This step is to ensure that no leaks are found in the hose between the AIR pump and the shut off valve. The shut off valve is spring loaded and requires air pressure to open for air to flow. A leak could prevent the valve from opening causing a no flow condition even though the pump is flowing air.

An open fuse for the ignition feed circuit could be caused by a short to ground in the components operated by the relay. Also check the wiring in the circuits on the switched side of the relay.

Step

Action

Values

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Install a scan tool.
Start the engine and allow it to run for 2 minutes.
Verify the engine is running at normal operating temperature and is in closed loop.
Command ON the AIR pump with the scan tool.

Does the short term fuel trim indicate a change of more than the specified value with 30 seconds?

16%

Go to Step 3

Go to Step 4

The condition is intermittent.

Are any DTCs stored?

Go to the applicable DTC table

Go to Diagnostic Aids

With the engine still running, command ON the AIR pump with the scan tool.
Observe the AIR pump clutch.

Is the AIR pump clutch engaged?

Go to Step 5

Go to Step 9

With the engine still running, command OFF the AIR pump with the scan tool.
Observe the AIR pump clutch.

Is the AIR pump clutch engaged?

Go to Step 6

Go to Step 19

Turn OFF the ignition.
Disconnect the AIR pump relay.
Connect a test lamp to the B+ terminal.
Probe the AIR pump relay control circuit with the test lamp.
Turn ON the ignition.

Is the test lamp ON?

Go to Step 7

Go to Step 8

Turn OFF the ignition.
Disconnect the VCM C1 connector.
Probe the AIR pump relay control circuit with the test lamp on the B+ terminal.

Is the test lamp ON?

Go to Step 30

Go to Step 36

Connect a test lamp to a ground.
Turn ON the ignition.
Probe the AIR pump feed circuit with the test lamp.

Is the test lamp ON?

Go to Step 31

Go to Step 33

Turn OFF the ignition.
Disconnect the AIR pump clutch connector.
Inspect for a poor connection at the AIR pump clutch. Refer to Diagnostic Aids.

Did you find a problem?

Go to Step 26

Go to Step 10

Turn ON the ignition leaving the engine OFF.
Probe the terminal for the AIR pump clutch feed circuit with a test lamp to a ground.
Command ON the AIR pump with the scan tool.

Is the test lamp ON?

Go to Step 11

Go to Step 12

Connect a test lamp to the B+ terminal.
Probe the terminal for the AIR pump clutch ground circuit.

Is the test lamp ON?

Go to Step 35

Go to Step 27

Turn OFF the ignition.
Disconnect the AIR pump relay.
Inspect for a poor connection at the AIR pump relay. Refer to Diagnostic Aids.

Did you find a problem?

Go to Step 26

Go to Step 13

Inspect for an open in the AIR pump clutch feed circuit between the relay and the clutch.

Did you find a problem?

Go to Step 26

Go to Step 14

Turn ON the ignition.
Probe both terminals for the ignition feed circuits at the AIR pump relay socket with a test lamp to a ground.

Is the test lamp ON at both terminals?

Go to Step 15

Go to Step 28

Connect a test lamp to the B+ terminal.
Probe the terminal for the AIR pump relay Control circuit with the test lamp.
Command ON the AIR pump with the scan tool.

Is the test lamp ON?

Go to Step 33

Go to Step 16

Turn OFF the ignition.
Disconnect the VCM C1 connector.
Inspect for a poor connection at the VCM. Refer to Diagnostic Aids.

Did you find a problem?

Go to Step 26

Go to Step 17

Inspect for an open in the AIR pump relay control circuit between the relay and the VCM.

Did you find a problem?

Go to Step 26

Go to Step 18

Turn ON the ignition.
Probe the terminal for the AIR pump relay control circuit with a test lamp to a ground.

Is the test lamp ON?

Go to Step 29

Go to Step 36

Turn OFF the ignition.
Disconnect the AIR output hose at the outlet of the AIR shut off valve.
Start the engine and allow it to idle.
Command ON the AIR pump with the scan tool.

Does air flow from the valve?

Go to Step 24

Go to Step 20

Turn OFF the ignition.
Disconnect the AIR pump output hose at the inlet of the AIR shut off valve.
Start the engine and allow it to idle.
Command ON the AIR pump with the scan tool.

Does air flow from the hose?

Go to Step 21

Go to Step 23

Command ON the AIR pump with the scan tool.
Accelerate the engine to approximately the specified value.

Does the air flow increase as the engine is accelerated?

1500 RPM

Go to Step 22

Go to Step 25

Inspect for leaks or loose connections on the hose between the AIR pump and the AIR shut off valve.

Did you find a problem?

Go to Step 32

Go to Step 34

Inspect for leaks or obstructions in the hose between the AIR pump and the AIR shut off valve.

Did you find a problem?

Go to Step 32

Go to Step 25

Inspect for leaks or restrictions on the following components:

•	AIR shut off valve

•

Hoses

•	Check valves

•

Fittings

•

AIR pipes

•	Exhaust manifolds

Did you find a problem?

Go to Step 32

Go to Diagnostic Aids

Inspect for a restriction or an obstruction in the inlet hose of the AIR pump.

Did you find a problem?

Go to Step 32

Go to Step 35

Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 37

Repair the open in the AIR pump clutch ground circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 37

Repair the open or short to ground in the ignition feed circuits to the AIR pump Relay. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 37

Repair the short to voltage on the AIR pump relay control circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 37

Repair the short to ground in the AIR pump relay control circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 37

Repair the short to voltage on the AIR pump clutch feed circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 37

Repair as necessary. Refer to Secondary Air Injection Check Valve and Check Valve Pipe Replacement .

Is the action complete?

Go to Step 37

Replace the AIR pump relay.

Is the action complete?

Go to Step 37

Replace the AIR shut off valve. Refer to Secondary Air Injection Check Valve and Check Valve Pipe Replacement .

Is the action complete?

Go to Step 37

Replace the AIR pump. Refer to Secondary Air Injection Pump Replacement .

Is the action complete?

Go to Step 37

Important: The replacement VCM must be programmed.

Replace the VCM. Refer to VCM Replacement/Programming .

Is the action complete?

Go to Step 37

Install a scan tool.
Start the engine and allow it to run for 2 minutes.
Verify the engine is running at normal operating temperature and is in closed loop.
Command ON the AIR pump with the scan tool.

Does the short term fuel trim indicate a change of more than the specified value with 30 seconds?

16%

System OK

Go to Step 4