Technical Description of OBD-II Trouble Code
The control circuit for the Coolant Pump “A” is experiencing high voltage.
What does that mean?
This particular diagnostic trouble code is applicable to all engines equipped with electric coolant pumps and OBDII technology. However, it is more commonly found in certain hybrid vehicles manufactured by Ford, Honda, Nissan, and Toyota.
The Coolant Pump A (CP-A) is typically located at the front or top of the engine, inside the wheel wells, or against the bulkhead. It is controlled by an electrical signal from the Powertrain Control Module (PCM).
The PCM receives various inputs, such as voltage signals from coolant temperature, intake air temperature, engine RPM, and air conditioning system pressure sensors. Based on these inputs, the PCM adjusts the signal sent to the CP-A.
The P2603 trouble code is usually triggered by electrical issues in the CP-A circuit. These issues should not be ignored during the troubleshooting process, especially if the problem is intermittent.
The troubleshooting steps may vary depending on the manufacturer, type of CP-A, and wire colors.
Other related trouble codes for the coolant pump “A” circuit include:
Symptoms & Severity
This trouble code usually has a severe impact on the cooling system, resulting in severe symptoms. Since it is primarily an electrical failure, the PCM cannot fully compensate for it. As a result, the cooling fans may operate continuously at 100% duty cycle.
Symptoms of a P2603 code may include:
Causes
The potential causes for this code to be set are:
Diagnostic and Repair Procedures
It is always recommended to check for technical service bulletins (TSB) specific to your vehicle. There may be a known issue with a known fix provided by the manufacturer, which can save time and money during diagnosis.
Next, locate the Coolant Pump B (CP-A) in your vehicle. It is usually found at the front or top of the engine, inside the wheel wells, or against the bulkhead. Once located, visually inspect the connector and wiring for any signs of scraping, rubbing, bare wires, burn spots, or melted plastic. Separate the connector and carefully examine the terminals inside for any signs of burning or corrosion. If necessary, clean the terminals using electrical contact cleaner and a plastic bristle brush. Apply electrical grease to the terminals before reconnecting.
If you have a scan tool, clear the diagnostic trouble codes from memory and check if the P2603 code returns. If it does not, the issue was most likely related to the connections.
For this particular code, the most common area of concern is the connections to the relays and the relays themselves, with a pump failure being the second most common cause.
If the code does return, further testing of the pump and associated circuits is necessary. Typically, there are 2 wires connected to each coolant pump. Start by disconnecting the harness going to the coolant pump. Using a Digital Volt Ohm Meter (DVOM), measure the resistance between the two terminals of the pump. It should not be open or shorted. Refer to the resistance specifications for your specific vehicle. If the pump motor is open or shorted, replace the coolant pump.
If the pump test passes, use a DVOM to check if there is 12V in the coolant pump power supply circuit (Red lead to the pump power supply circuit, black lead to a good ground). Activate the coolant pump using a scan tool. If there is no 12 volts reaching the pump, repair the wiring from the PCM or relay to the pump, or consider the possibility of a faulty PCM.
If the power supply circuit is functioning properly, check if there is a good ground at the coolant pump. Connect a test light to the positive terminal of a 12V battery and touch the other end of the test light to the ground circuit going to the coolant pump. Use the scan tool to activate the coolant pump and observe if the test light illuminates each time the pump is activated. If the test light does not illuminate, there is a problem with the circuit. If it does illuminate, wiggle the wiring harness going to the pump to check for any intermittent connections indicated by flickering of the test light.
If all previous tests have passed and the P2603 code persists, it is likely that the coolant pump has failed. However, a failed PCM cannot be ruled out until the coolant pump is replaced. If unsure, seek assistance from a trained automotive diagnostician. Remember that PCMs must be programmed or calibrated to the vehicle for correct installation.
Other similar coolant pump codes include P261A, P261B, P261C, and P261D.
