Broken, chafed, or disconnected wire in the coolant bypass valve control circuit; Corroded or loose electrical connector at the valve or PCM; Failed coolant bypass valve solenoid or actuator (open internal coil); Faulty PCM driver for the control circuit (rare but possible); Coolant intrusion into the valve connector or actuator, causing corrosion and an open circuit; Aftermarket or incorrect valve installed that does not match the PCM's expected resistance

DTC codes / P0Exx · Hybrid propulsion / P0E73

P0E73Coolant Bypass Valve A Control Circuit/Open

Q: What does code P0E73 mean?

Coolant Bypass Valve A Control Circuit/Open. P0E73 indicates that the powertrain control module (PCM) has detected an open circuit or excessive resistance in the control circuit for the coolant bypass valve, which is used to manage coolant flow for faster engine warm-up and improved efficiency. The PCM commands the valve to move and monitors the circuit for expected electrical feedback, but the signal is missing or out of range, so it sets this code and may default to a fail-safe cooling strategy.

P0E73 indicates that the powertrain control module (PCM) has detected an open circuit or excessive resistance in the control circuit for the coolant bypass valve, which is used to manage coolant flow for faster engine warm-up and improved efficiency. The PCM commands the valve to move and monitors the circuit for expected electrical feedback, but the signal is missing or out of range, so it sets this code and may default to a fail-safe cooling strategy.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaHybrid propulsion

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Longer than normal engine warm-up times, especially in cold weather
Reduced fuel economy due to the engine running richer for extended periods
Inconsistent cabin heater performance, with lukewarm air until the engine fully warms
Possible overheating if the valve fails in a position that restricts coolant flow
In some vehicles, a message on the driver information center indicating a cooling system fault

Common causes, most likely first

Broken, chafed, or disconnected wire in the coolant bypass valve control circuit
Corroded or loose electrical connector at the valve or PCM
Failed coolant bypass valve solenoid or actuator (open internal coil)
Faulty PCM driver for the control circuit (rare but possible)
Coolant intrusion into the valve connector or actuator, causing corrosion and an open circuit
Aftermarket or incorrect valve installed that does not match the PCM's expected resistance

How to diagnose and fix it

Inspect the coolant bypass valve connector and wiring for damage, corrosion, or looseness, and repair as needed
Measure the resistance of the valve solenoid with a multimeter and compare to the manufacturer's specification to check for an open coil
Check for continuity and short-to-ground or short-to-power on the control circuit between the valve and PCM, repairing any wiring faults
Test the valve actuator with a bidirectional scan tool to command it open and closed while observing circuit feedback or listening for movement
If the valve fails to respond and wiring is good, replace the coolant bypass valve
Clear the diagnostic trouble codes and perform a road test to verify the repair and ensure the code does not return
If the code persists after all other checks, diagnose the PCM control circuit driver or consult a dealer for reprogramming or replacement

Don't Overlook the Coolant Bypass Valve Circuit

A common oversight is assuming the valve itself is defective when the real problem is a corroded connector pin or a wire rubbed through by engine vibration, so always perform a thorough visual and electrical inspection first.
This code can be set by a valve that is mechanically stuck but electrically intact, so a resistance check alone may not reveal the fault; command the valve with a scan tool to confirm movement.
On some vehicles, the coolant bypass valve is part of a larger thermostat housing assembly, and replacing just the solenoid may not be possible, leading to higher repair costs than expected.
A failing coolant temperature sensor can cause the PCM to command the bypass valve incorrectly, but that would typically set a different code; however, always check live data to ensure the PCM is not misinterpreting conditions.
After replacing the valve, some vehicles require a coolant bleed procedure and a relearn of the valve's end stops using a scan tool, otherwise the code may return immediately.

Can I keep driving with P0E73?

You can generally drive the vehicle with this code, but avoid extended idling and monitor the temperature gauge closely, as a stuck valve can cause overheating or poor heater performance. If the engine temperature rises above normal or you see steam, stop and have the vehicle towed to prevent engine damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.