P279B – All-Wheel Drive Low Range Performance

P279B Possible Causes

Faulty Engine Control Module (ECM)
Engine Control Module (ECM) harness is open or shorted
Poor electrical connection in Engine Control Module (ECM) circuit

How to Fix Code P279B

Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Look for damaged components and check for broken, bent, pushed out, or corroded connector pins.

Possible Symptoms

Illuminated engine light (or service engine soon warning light)

P279B Meaning

The Engine Control Module (ECM) uses the following two methods to determine whether the transfer case is in 4WD Low, 4WD High, or Neutral.
1. The first method is to compare the transmission output speed sensor with the transfer case output speed sensor to calculate the transfer case range.

2. The second method is to use a LAN message sent from the transfer case shift control module to the ECM.

The ECM uses this message to determine required engine torque and transmission shifting.
Internal fault detection is handled within the control module. No external circuit diagnosis is involved.

P279C – Four-Wheel Drive Neutral Range Performance

P279C Possible Causes

Faulty Engine Control Module (ECM)
Engine Control Module (ECM) harness is open or shorted
Poor electrical connection in the Engine Control Module (ECM) circuit

How to Fix Code P279C

Possible Symptoms

Illuminated engine light (or service engine soon warning light)

P279C Meaning

The Engine Control Module (ECM) uses the following two methods to determine whether the transfer case is in 4WD Low, 4WD High, or Neutral.
1. The first method involves comparing the transmission output speed sensor to the transfer case output speed sensor to calculate the transfer case range.

2. The second method uses a LAN message sent from the transfer case shift control module to the ECM.

The ECM uses this message to determine required engine torque and transmission shifting.

Internal fault detection is handled within the control module. No external circuit diagnostics are involved.

P279D – Four-Wheel Drive Range Signal Circuit

P279D Possible Causes

Faulty all-wheel drive range chain
Four-wheel drive range harness is open or shorted
Poor electrical connection in the four-wheel drive range circuit

How to Fix Code P279D

Check the “Possible Causes” listed above. Visually inspect the wiring harness and related connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

Possible Symptoms

Check Engine Light illuminated (or Service Engine Soon warning light)

P279D Meaning

The Transmission Control Module (TCM) monitors the signal from the four-wheel drive range signal circuit. The TCM sets the OBDII code when the four-wheel drive transmission range signal circuit signal is outside factory specifications.

P279E – Signal Circuit Range/Performance of the Four-Wheel Drive System

P279E Possible Causes

Faulty all-wheel drive transfer chain
All-wheel drive range circuit wiring harness open or shorted
Poor electrical connection in the all-wheel drive range circuit

How to Fix Code P279E

Possible Symptoms

Check engine light illuminated (or service engine soon warning light)

P279E Meaning

The Transmission Control Module (TCM) monitors the signal from the all-wheel drive range signal circuit. The TCM sets the OBDII code when the all-wheel drive transfer range signal circuit signal is outside factory specifications.

P279F – Low All-Wheel Drive Range Signal Circuit

P279F Possible Causes

Faulty all-wheel drive transfer chain
Four-wheel drive range harness is open or shorted
Poor electrical connection in the four-wheel drive range circuit

How to Fix Code P279F

Possible Symptoms

Check Engine Light illuminated (or Service Engine Soon warning light)

P279F Meaning

The Transmission Control Module (TCM) monitors the signal from the four-wheel drive range signal circuit. The TCM sets the OBDII code when the four-wheel drive transfer range signal circuit signal is outside factory specifications.

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P27A0 – High Traction Range Signal Circuit

P27A0 Possible Causes

Faulty all-wheel drive powertrain
Four-wheel drive range harness is open or shorted
Poor electrical connection in the four-wheel drive range circuit

How to Fix Code P27A0

Possible Symptoms

Check engine light illuminated (or service engine soon warning light)

P27A0 Meaning

P2600 – Open Coolant Pump Control Circuit

Symptoms and Severity

The severity is generally serious due to its impact on the cooling system. Since it is typically an electrical failure, the PCM cannot fully compensate for it. Partial compensation usually means the cooling fans run all the time (100% duty cycle).

Symptoms of a P2600 code may include:

Malfunction indicator light illuminated
Overheating
The air conditioning system not working properly

Causes

Potential causes for setting this code are as follows:

Open in the coolant pump circuit – likely
Faulty coolant pump – electrically failed open circuit – likely
Failed PCM – unlikely

Diagnostic and Repair Procedures

A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your issue may be a known problem with a known fix published by the manufacturer and can save you time and money during diagnosis.

Next, locate the B coolant pump (CP-A) on your specific vehicle. This pump is typically found mounted at the front of the engine, on top of the engine, inside the wheel wells, or against the firewall. Once located, visually inspect the connector and wiring. Look for scratches, rubbing, bare wires, burns, or melted plastic. Disconnect the connector and carefully inspect the terminals (the metal parts) inside the connector. See if they appear burnt or have a greenish tint indicating corrosion. Use electrical contact cleaner and a plastic-bristled brush if cleaning the terminals is necessary. Let it dry and apply electrical grease where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from memory and see if the P2600 code returns. If it does not, the connections were likely your problem.

For this particular code, this is the most common area of concern, as are the relays/connections to the relays, with a pump failure being the second most common.

If the code returns, we will need to test the pump and related circuits. Typically, there are 2 wires at each coolant pump. First, disconnect the harness going to the coolant pump. With a digital volt-ohm meter (DVOM), connect one meter lead to one terminal of the pump. Connect the remaining meter lead to the other pump terminal. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the pump motor is open or shorted (infinite resistance or no resistance/0 ohms), replace the coolant pump.

If this test passes, with a DVOM, check that you have 12V at the coolant pump power circuit (red lead to the pump power circuit, black lead to a good ground). With a scan tool that can activate the coolant pump, turn on the coolant pump. If there is no 12 volts at the pump, repair the wiring from the PCM or relay to the pump, or possibly a faulty PCM.

If that checks out, verify the coolant pump ground circuit. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the coolant pump circuit ground. Using the scan tool to actuate the coolant pump, check if the test light illuminates each time the scan tool actuates the pump. If the test light does not illuminate, it would indicate a circuit problem. If it does light up, wiggle the wire harness going to the pump to see if the test light flickers, indicating an intermittent connection.

If all previous tests have passed and you continue to get a P2600, it would most likely indicate a failing coolant pump, although a faulty PCM cannot be ruled out until the coolant pump has been replaced. If in doubt, seek assistance from a qualified automotive diagnostician. PCMs need to be programmed or calibrated to the vehicle to be installed properly.

Other similar coolant pump codes include P261A, P261B, P261C, and P261D.

P2601 Coolant Pump Control Circuit Performance

Symptoms and Severity

Severity is generally high due to its impact on the cooling system. Since it can be an electrical or mechanical failure, the PCM cannot fully compensate for it. Partial compensation usually means the cooling fans run continuously (100% duty cycle).

Symptoms of a P2601 code may include:

Malfunction indicator light illuminated
Overheating
Air conditioning system not functioning properly

Causes

Potential causes for this code being set are:

Open circuit in the coolant pump – likely
Coolant pump failure – inoperative (mechanically or electrically) – probable
PCM failure – unlikely

Diagnostic and Repair Procedures

A good starting point is always to check the technical service bulletins (TSBs) for your specific vehicle. Your issue might be a known problem with a published manufacturer fix, which can save time and money during diagnosis.

Next, locate the B coolant pump (CP-A) on your specific vehicle. This pump is typically mounted at the front of the engine, on top of the engine, inside the wheel wells, or against the firewall. Once located, visually inspect the connector and wiring. Look for scratches, rubbing, exposed wires, burns, or melted plastic. Disconnect the connector and carefully inspect the terminals (the metal parts) inside. Check if they appear burnt or have a greenish tint indicating corrosion. Use electrical contact cleaner and a plastic-bristled brush if terminal cleaning is needed. Allow to dry and apply electrical grease where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from memory and see if the P2601 code returns. If not, connections were likely your issue.

For this particular code, this is the most common area of concern, along with relay/relay connections, with pump failure being the second most common.

If the code returns, we’ll need to test the pump and related circuits. Typically, there are 2 wires for each coolant pump. First, disconnect the harness going to the coolant pump. With a digital volt ohm meter (DVOM), connect one meter lead to one pump terminal. Connect the remaining meter lead to the other pump terminal. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the pump motor is open or shorted (infinite resistance or no resistance/0 ohms), replace the coolant pump.

If this test passes, use a DVOM to verify you have 12V at the coolant pump power circuit (red lead to pump power circuit, black lead to a good ground). With a scan tool capable of activating the coolant pump, turn on the coolant pump. If there’s no 12 volts at the pump, repair the wiring from the PCM or relay to the pump, or possibly a faulty PCM.

If that checks out, verify the coolant pump is properly grounded. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the coolant pump circuit ground. Using the scan tool to activate the coolant pump, check if the test light illuminates each time the scan tool activates the pump. If the test light does not illuminate, it would indicate a circuit problem. If it lights up, wiggle the wiring harness going to the pump to see if the test light flickers, indicating an intermittent connection.

If all previous tests pass and you continue to get a P2601, it would most likely indicate a failing coolant pump, although a faulty PCM cannot be ruled out until the coolant pump has been replaced. When in doubt, seek assistance from a qualified automotive diagnostician. PCMs need to be programmed or calibrated to the vehicle to be installed correctly.

Other similar coolant pump codes include P261A, P261B, P261C, and P261D.

P2602 Coolant Pump A Control Circuit Low

Symptoms

and Severity

The severity is generally high due to its impact on the cooling system. Since it is typically an electrical failure, the PCM cannot fully compensate for it. Partial compensation usually means the cooling fans run continuously (100% duty cycle).

Symptoms of a P2602 code may include:

Malfunction indicator light illuminated
Overheating
Air conditioning system not functioning properly

Causes

Potential causes for this code are as follows:

Open circuit in the coolant pump – likely
Failed coolant pump – likely
Failed PCM – unlikely

Diagnostic and Repair Procedures

A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your issue might be a known problem with a published fix from the manufacturer, which can save time and money during diagnosis.

Next, locate the B coolant pump (CP-A) on your specific vehicle. This pump is typically mounted at the front of the engine, on top of the engine, inside the wheel wells, or against the firewall. Once located, visually inspect the connector and wiring. Look for scratches, rubbing, exposed wires, burns, or melted plastic. Disconnect the connector and carefully inspect the terminals (the metal parts) inside. Check if they appear burnt or have a greenish tint indicating corrosion. Use electrical contact cleaner and a plastic-bristled brush if terminal cleaning is necessary. Allow it to dry and apply electrical grease where the terminals make contact.

If you have a scan tool, clear the diagnostic codes from memory and see if the P2602 code returns. If it does not, the connections were likely the issue.

For this particular code, the most common area of concern is the relays and relay connections, with pump failure being the second most common.

If the code returns, we will need to test the pump and related circuits. Typically, there are 2 wires for each coolant pump. First, disconnect the harness going to the coolant pump. With a digital volt-ohm meter (DVOM), connect one meter lead to one terminal of the pump. Connect the remaining meter lead to the other pump terminal. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the pump motor is open or shorted (infinite resistance or no resistance/0 ohms), replace the coolant pump.

If this test passes, use a DVOM to check for 12V at the coolant pump power circuit (red lead to the pump power circuit, black lead to a good ground). With a scan tool capable of activating the coolant pump, turn on the coolant pump. If there is no 12 volts at the pump, repair the wiring from the PCM or relay to the pump, or possibly a faulty PCM.

If that is okay, check the coolant pump ground circuit. Connect a test light to the positive 12V battery terminal (red terminal) and touch the other end of the test light to the ground circuit going to the coolant pump circuit ground. Using the scan tool to activate the coolant pump, check if the test light illuminates each time the scan tool activates the pump. If the test light does not illuminate, it would indicate a circuit problem. If it does light up, wiggle the wiring harness going to the pump to see if the test light flickers, indicating an intermittent connection.

If all previous tests pass and you continue to get a P2602, it would most likely indicate a faulty coolant pump, although a faulty PCM cannot be ruled out until the coolant pump has been replaced. If in doubt, seek assistance from a qualified automotive diagnostician. PCMs need to be programmed or calibrated to the vehicle to be installed correctly.

Other similar coolant pump codes include P261A, P261B, P261C, and P261D.