P0C23 — Auxiliary Transmission Fluid Pump Control Module Circuit/Open #

The definition of this code may vary depending on the vehicle manufacturer. Always refer to your OEM (Original Equipment Manufacturer) service documentation for specific details.

• Auxiliary Transmission Fluid Pump Control Module Circuit/Open (Generic/SAE)
• Hybrid Transmission Auxiliary Fluid Pump Control Circuit/Open (Toyota/Lexus)
• Auxiliary Transmission Fluid Pump Module Circuit Malfunction (GM/Chevrolet)
• AUX PUMP CTRL MOD CIRCUIT OPEN (Ford/Lincoln)

Summary of code P0C23 #

The P0C23 diagnostic trouble code (DTC) signals an electrical issue in the control circuit related to the Auxiliary Transmission Fluid Pump Control Module. This system is typically present in hybrid and some advanced automatic transmissions, where an auxiliary pump ensures transmission lubrication and cooling when the main engine-driven pump is inactive—such as during electric-only driving or start-stop events. The code generally points to a circuit that is open—meaning there’s a break or fault interrupting proper electrical flow. If this code is present, the vehicle’s control module has detected an abnormality, like a disconnected wire or failed component, within the auxiliary pump’s control circuit. Drivers should address this promptly to avoid potential transmission damage, especially in vehicles that rely heavily on the auxiliary pump for low-speed or electric operation.

Common symptoms for code P0C23 #

When the P0C23 code is set, symptoms can range from subtle to severe, depending on the vehicle’s design and operating conditions. Some drivers may not notice immediate changes, while others could experience obvious performance issues, especially during electric or low-speed operation.

• Illuminated or flashing Check Engine Light
• Transmission may default to limp mode (reduced performance)
• Erratic or harsh shifting
• Possible overheating transmission warning
• Unusual noises from the transmission area
• Reduced fuel efficiency in hybrid vehicles

Most probable causes of P0C23 #

The P0C23 code is most often triggered by electrical or component failures within the auxiliary pump circuit. Some causes are more common than others; in most cases, technicians find issues with wiring or connectors, but module or pump failures do occur.

1. Damaged or corroded electrical connectors at the auxiliary pump or control module
2. Broken, shorted, or open wiring in the control circuit
3. Faulty Auxiliary Transmission Fluid Pump Control Module
4. Defective auxiliary transmission fluid pump itself
5. Blown fuse or failed relay associated with the auxiliary pump circuit
6. PCM/TCM (Powertrain or Transmission Control Module) internal fault (rare)

Step-by-step diagnosis for code P0C23 #

Diagnosing a P0C23 code requires a logical, step-by-step approach to rule out common electrical issues before considering component replacement. Always follow safety precautions when working with high-voltage hybrid systems.

• Scan for additional DTCs: Check for related codes (e.g., battery, transmission, wiring errors) that may point to an underlying cause.
• Inspect fuses and relays: Locate and test the fuses and relays associated with the auxiliary pump circuit.
• Visually inspect wiring and connectors: Look for damaged, corroded, or loose connectors at the pump, control module, and battery junctions.
• Check for open circuits: Use a multimeter to test for continuity in the control module and pump wiring.
• Test the auxiliary pump and module: Bench-test the auxiliary pump and its control module according to OEM procedures.
• Check for control module updates: Some OEMs issue software updates or recalls; check service bulletins.
• Clear codes and retest: After repairs, clear the DTC and perform a road test to confirm resolution.

Possible repairs for code P0C23 #

The correct repair depends on what is found during diagnosis. Most issues with P0C23 are resolved by addressing wiring or connector faults, but component replacement may be necessary if the pump or module fails testing.

• Repair or replace damaged wiring in the auxiliary pump circuit
• Clean, repair, or replace corroded connectors
• Replace blown fuse or faulty relay supplying power to the pump
• Replace faulty auxiliary transmission fluid pump control module
• Replace defective auxiliary transmission fluid pump
• Reflash or replace PCM/TCM if found faulty (rare)

Can you drive with code P0C23? #

Driving is generally NOT recommended when code P0C23 is present, especially in hybrid or start-stop equipped vehicles. The auxiliary transmission fluid pump is critical for proper lubrication and cooling during certain driving conditions. Ignoring this code can lead to transmission damage, overheating, or unexpected loss of vehicle performance. If driving is absolutely necessary, limit distance and avoid heavy loads or high temperatures until the issue is resolved.

Vehicles most commonly affected by P0C23 #

This code appears most frequently in hybrid vehicles and select modern automatics where auxiliary fluid pumps are used. OEMs commonly affected include:

• Toyota and Lexus hybrids (Prius, Camry Hybrid, Highlander Hybrid, etc.)
• General Motors (Chevrolet Volt, Malibu Hybrid, various Cadillac models)
• Ford and Lincoln (Fusion Hybrid, C-Max, Lincoln MKZ Hybrid)
• Chrysler/Jeep (Pacifica Hybrid, Jeep Wrangler 4xe)
• Honda/Acura (Accord Hybrid, Clarity, MDX Hybrid)

Common errors & best practices for P0C23 #

It’s easy to misdiagnose P0C23 if you skip basic checks or jump to component replacement. Best practice is to always follow a thorough, methodical diagnostic process—don’t just replace the pump or module without confirming the true fault.

• Overlooking simple wiring or connector issues
• Replacing the pump without checking for open circuits
• Neglecting to inspect fuses and relays
• Ignoring OEM service bulletins or software updates
• Not clearing codes and rechecking after repair

Express FAQ for code P0C23 #

Here are quick answers to frequent questions about the P0C23 code:

• Q: Will P0C23 cause my vehicle to stop running?
  A: Not usually, but it can cause performance issues or transmission overheating. If ignored, serious transmission damage is possible.
• Q: Can I fix P0C23 myself?
  A: If you’re comfortable checking fuses and connectors, you may address minor issues. For wiring repairs or component replacement, professional help is recommended—especially in hybrid vehicles due to high-voltage risks.