P2602 Coolant Pump "A" Control Circuit Low

The P2602 diagnostic trouble code indicates that the engine control module has detected a voltage level below the expected range in the control circuit of Coolant Pump "A".

Electric coolant pumps are used to circulate coolant through the engine and, depending on the vehicle, through additional cooling circuits. The pump may be controlled according to engine temperature, operating conditions, turbocharger requirements, cabin heating demands, or the thermal management requirements of hybrid and other electrified systems.

When the control module detects that the electrical condition of the Coolant Pump "A" control circuit is lower than expected, it can store P2602.

This does not automatically mean that the coolant pump itself has failed. Low voltage can be caused by a problem with the power supply, excessive resistance in the circuit, a poor ground connection, damaged wiring, a faulty connector, a fuse or relay problem, or an internal electrical fault in the pump.

What Does P2602 Mean?

P2602 is fundamentally an electrical circuit fault.

The control module monitors the electrical condition of the Coolant Pump "A" circuit and expects the circuit to operate within a specified range. If the monitored voltage or control signal falls below the manufacturer's expected threshold, P2602 may be stored.

A voltage drop can occur at several points in the circuit. A cable may have excessive resistance, a connector terminal may have poor contact, a relay may have damaged contacts, or the pump itself may have an internal electrical problem.

For this reason, simply checking whether the pump runs is not always enough. The circuit should also be tested while the pump is operating or being commanded on.

What Is Coolant Pump "A"?

"Coolant Pump A" is a manufacturer-defined designation for a specific electrically controlled coolant pump.

The exact pump identified as "A" can vary between vehicle manufacturers and models. It may be the main electric coolant pump or an auxiliary pump used for a particular cooling circuit.

Depending on the vehicle, an electric coolant pump may be used for:

• Main engine cooling

• Turbocharger cooling

• Heater circuits

• Hybrid battery cooling

• Power electronics cooling

• Coolant heat storage systems

• After-run cooling

• Other auxiliary thermal-management functions

Therefore, the first step in diagnosing P2602 is to determine which pump the vehicle manufacturer identifies as Coolant Pump "A".

Common Causes of P2602

P2602 can be caused by a problem anywhere in the electrical circuit associated with the coolant pump.

Voltage drop in the power supply

A high-resistance connection or damaged cable can cause the voltage reaching the pump to fall when the pump is operating.

The battery may have normal voltage while the pump receives significantly less voltage under load.

High resistance in the wiring

Partially damaged wires, corroded conductors, poor terminal connections, or damaged splice points can restrict current flow and create an abnormal voltage condition.

Connector or terminal problems

Loose, corroded, pushed-back, or damaged terminals can create resistance in the pump circuit.

Because coolant pumps are often located in areas exposed to heat, moisture, dirt, and vibration, connector problems should be carefully inspected.

Poor ground connection

A weak ground can prevent the pump from receiving the electrical conditions it needs to operate correctly.

A ground connection may look clean and secure but still have excessive resistance when the pump is operating. A voltage-drop test can help identify this type of problem.

Fuse problem

A blown fuse can interrupt the pump's power supply. However, the fuse itself is not always the problem.

A poor connection at the fuse holder can also create resistance and cause voltage loss when the pump is operating.

Relay failure

If the pump receives power through a relay, worn or burned relay contacts can create excessive resistance.

The relay may appear to work normally but still cause a significant voltage drop under load.

Internal coolant pump failure

The electric motor or internal electronics of the coolant pump can fail.

A mechanically restricted pump may also draw abnormal current, affecting the electrical behavior of the circuit.

Short circuit

A short to ground or another electrical circuit can pull the control circuit below its expected voltage level.

Depending on the circuit design, this may also cause a blown fuse or additional diagnostic trouble codes.

Control circuit fault

Some modern electric coolant pumps are electronically controlled rather than being simple two-wire motors.

A problem with the control signal, wiring, or communication between the pump and the control module can therefore also result in P2602.

Symptoms of P2602

The symptoms depend largely on the function of Coolant Pump "A" in the particular vehicle.

Possible symptoms include:

• Check Engine Light

• Cooling system warning

• Coolant pump not operating

• Intermittent pump operation

• Higher-than-normal engine temperature

• Engine overheating

• Reduced heater performance

• Cooling fan operating more frequently or for longer periods

• Unusual noise from the coolant pump

• Reduced engine performance in some vehicles

• Fail-safe or reduced-power operation

Not every vehicle will experience all of these symptoms.

If Pump A is part of an auxiliary cooling circuit, the vehicle may continue to operate normally even though P2602 is stored.

If the pump is responsible for a major part of the engine cooling system, however, the consequences can be much more serious.

Can P2602 Cause Engine Overheating?

Yes, it can, depending on the role of Coolant Pump "A".

If the affected pump is responsible for an important part of the engine cooling system and its electrical supply is too low for proper operation, coolant circulation can be reduced.

This can cause engine temperature to rise, particularly under heavy load, at low vehicle speeds, or in hot ambient conditions.

If the vehicle is showing an overheating warning, the temperature gauge is rising abnormally, or coolant is being lost, continued driving should be avoided until the cooling system has been inspected.

How Is P2602 Diagnosed?

A proper diagnosis should determine why the circuit voltage is low rather than simply replacing the coolant pump.

The diagnostic process generally begins by scanning the vehicle for all stored and pending trouble codes and reviewing the freeze-frame information.

The technician should then identify the exact Coolant Pump "A" and examine its electrical circuit using the manufacturer's wiring diagram and specifications.

Check the Power Supply

The voltage at the coolant pump should be measured.

The important point is that the measurement should not necessarily be limited to a simple ignition-on voltage check.

The pump should be tested under the conditions in which it is commanded to operate.

For example, the battery may show normal voltage while the pump connector shows significantly lower voltage when the pump is operating.

This difference can indicate excessive resistance in the power supply circuit.

Check the Ground

The pump's ground circuit should also be tested.

A poor ground connection can produce symptoms similar to a low supply voltage.

A voltage-drop test performed while the pump is operating can determine whether excessive resistance exists in the ground path.

The exact acceptable voltage-drop limit should always be taken from the vehicle manufacturer's service information.

Perform a Voltage-Drop Test

Voltage-drop testing is particularly useful when diagnosing P2602.

A cable or connection can appear perfectly normal when there is little or no current flowing through it. Once the pump is operating and current increases, however, resistance in that connection can produce a significant voltage drop.

The test should therefore be performed under load whenever the manufacturer's diagnostic procedure calls for it.

This can help identify problems in:

• Power cables

• Ground cables

• Relay contacts

• Fuse holders

• Connectors

• Terminals

• Wiring splices

Inspect the Wiring and Connector

The coolant pump connector should be disconnected and inspected carefully.

Look for:

• Corrosion

• Moisture

• Loose terminals

• Bent terminals

• Terminals pushed back inside the connector

• Burn marks

• Melted plastic

• Damaged wiring

• Poor terminal-to-wire connections

The wiring should also be inspected along its entire route.

Heat from the engine, turbocharger, exhaust components, or other hot parts can damage insulation and wiring over time.

Check the Fuse and Relay

The pump fuse should be inspected and tested.

If the fuse is blown, the cause should be identified before simply installing another fuse.

A short circuit or an internal pump failure may cause the fuse to fail repeatedly.

If a relay is used, its operation and voltage drop across the contacts should also be checked.

A relay can click and appear to function while its contacts still have excessive resistance.

Test the Coolant Pump

If supported by the vehicle, a suitable diagnostic scan tool can be used to command the coolant pump on.

The pump's response should then be observed.

If the pump does not operate, the technician should determine whether the problem is caused by a missing power supply, poor ground, missing control signal, wiring fault, or an internal pump failure.

If the pump does operate but P2602 returns, the pump should still be tested under operating conditions.

Its supply voltage, ground, control signal, and current draw may provide important diagnostic information.

What If the Pump Still Works?

A working pump does not automatically rule out a problem with the pump or its circuit.

For example, an electric motor may still run while drawing abnormal current.

Likewise, a weak connector can allow the pump to operate under light conditions but cause a significant voltage drop when the electrical load increases.

This is why a visual inspection or simple functional test may not be enough to diagnose P2602.

Can P2602 Be Intermittent?

Yes.

Electrical problems can cause P2602 to appear intermittently.

A loose terminal may lose contact because of engine vibration. A partially broken wire may change resistance as the harness moves.

Temperature can also influence the problem. A connection may work normally when cold but develop greater resistance as the engine compartment becomes hot.

Moisture and corrosion can create similar intermittent problems.

For this reason, clearing the code and finding that it does not immediately return does not necessarily mean the problem has been fixed.

Should the Coolant Pump Be Replaced Immediately?

No.

P2602 by itself does not prove that the coolant pump has failed.

Before replacing the pump, the electrical circuit should be checked, including:

• Power supply

• Ground

• Voltage drop

• Fuse

• Relay

• Connector

• Terminals

• Wiring

• Control signal

• Pump current draw

If testing confirms an internal fault in the pump, replacement may be necessary.

If the actual problem is a damaged wire, poor connector, faulty relay, or bad ground, replacing the pump will not solve the underlying fault.

Can You Drive With P2602?

Whether the vehicle can be driven depends on the function of Coolant Pump "A" and the symptoms present.

If the affected pump is used only for an auxiliary cooling circuit, the engine may continue to operate normally for some time.

If the pump is important to the main engine cooling system, however, continued operation can lead to overheating.

The vehicle should not be driven if there is:

• Rising engine temperature

• An overheating warning

• Coolant loss

• Steam from the engine compartment

• Sudden loss of cabin heat accompanied by cooling-system symptoms

• Abnormal cooling fan behavior together with increasing engine temperature

Even when the engine temperature appears normal, the cause of P2602 should be diagnosed because the pump may be required under conditions that have not yet occurred.

How Is P2602 Repaired?

The repair depends entirely on the cause identified during diagnosis.

A failed coolant pump must be replaced.

Damaged or corroded wiring should be repaired or replaced.

A damaged connector or terminal should be properly repaired.

A faulty relay should be replaced.

A poor ground connection should be cleaned or repaired.

A blown fuse should only be replaced after determining why it failed.

If all external components and wiring have been tested and the control module itself is found to be defective, the module may require repair, replacement, or programming according to the manufacturer's procedures.

The Most Important Diagnostic Point for P2602

The important question with P2602 is not simply "Is the coolant pump bad?"

The more useful question is:

"Why is the voltage in the Coolant Pump 'A' control circuit lower than expected?"

The answer may be the pump itself, but it may also be found in the power supply, ground circuit, wiring, relay, fuse, connector, or control circuit.

A proper diagnosis therefore requires more than checking whether the pump turns on.

Testing the circuit under load, measuring voltage drop, checking the ground, inspecting the connectors, and evaluating the pump's electrical behavior can help identify the actual source of the fault.

Because the exact electrical architecture and voltage thresholds vary by vehicle, measurements should always be compared with the manufacturer's specifications for that particular model.