P0C23 — Auxiliary Transmission Fluid Pump Control Module Circuit/Open
powertrain (engine/transmission)
Is it safe to drive?
Drive with caution Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.
How to diagnose with an OBD scanner
- Read the code and freeze frame Connect an OBD2 scanner, confirm P0C23 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
- Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
- Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
- Subsystem check Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
- Subsystem check Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
- Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P0C23 does not return.
Approximate repair cost
Repair cost depends on which component actually failed. Typical scenarios for P0C23 (parts and labor, USD, independent shop rates): Transmission rebuild or replacement: $2,500–$5,500; Valve body repair or replacement: $700–$1,500; Transmission fluid service: $150–$350; Replace a shift solenoid: $300–$800. Overall, fixing P0C23 usually costs between $150 and $5,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.
Common questions
Will P0C23 clear itself?
Sometimes P0C23 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.
Is it safe to drive with P0C23?
Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.
How much does it cost to fix P0C23?
Transmission rebuild or replacement — $2,500–$5,500; Valve body repair or replacement — $700–$1,500; Transmission fluid service — $150–$350; Replace a shift solenoid — $300–$800. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.
How do I diagnose P0C23 myself?
Start with a scan: confirm P0C23, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the automatic transmission control, and verify the suspect component against live data before buying parts.
What is the most common cause of P0C23?
The most common causes are: wiring or connector faults in the valve body harness, valve body wear, failed shift or pressure control solenoid.
P0C23 indicates the powertrain control module has detected an electrical fault in the circuit that operates the auxiliary transmission fluid pump. This secondary pump supplements the main pump during low-speed maneuvering, idle, and when the engine restarts after an auto-stop event. It ensures hydraulic pressure stays high enough for smooth gear engagements even when the engine is barely turning. When the module sends a command to this pump circuit and the electrical response falls outside factory specifications—too little voltage, an open circuit, or abnormal resistance—it logs P0C23.
The module evaluates this circuit every driving cycle. It takes more than a single bad reading to trigger the light; the fault must repeat across multiple cycles before the check engine lamp illuminates. When P0C23 is stored, the accompanying freeze frame snapshot records engine speed, load, coolant temperature, and vehicle speed at the moment the problem occurred. That snapshot is your best clue to whether the fault shows up at idle, under hard acceleration, or at highway cruising speed.
Symptoms of P0C23
The auxiliary pump fault disrupts hydraulic pressure regulation, and transmission behavior changes accordingly. You may notice the transmission shifting roughly or with noticeable hesitation between gears. The check engine or transmission warning lamp typically appears on the instrument cluster. Gear slipping—where the engine revs without a corresponding increase in road speed—signals that clutch packs are not being held at proper line pressure. In some cases the transmission locks into a single gear as a protective limp mode. At the severe end of the spectrum the vehicle refuses to move at all. Highway-speed shuddering is another indicator that the pump is not maintaining steady pressure.
Common Causes
The most frequent trigger for P0C23 is damaged wiring or connectors in the valve body harness. Broken insulation, corroded terminals, loose plugs, or water intrusion at the connector can interrupt the electrical signal to the pump module. Shift solenoids and pressure control solenoids are also common culprits; they can short, open, or leak internally. Internal mechanical wear in clutches or the torque converter can degrade fluid pressure and confuse the module into flagging a circuit fault. Low or contaminated transmission fluid is a straightforward cause that warrants attention before assuming electronic failure. Valve body wear—particularly scoring on the bore surfaces that house the solenoids—can create pressure leaks. A failing transmission speed sensor may also produce codes that mask the root electrical problem.
How to Diagnose P0C23
A systematic approach prevents unnecessary parts replacement. First, connect a scan tool and confirm P0C23 is active; save the freeze frame data and note the conditions recorded when the fault set. Next, pull any related trouble codes from the transmission and powertrain controllers—other stored codes often point directly to the faulty component. Check for manufacturer TSBs covering your specific make and model; the factory may have released a software update or known repair procedure for this code. Then perform a close visual inspection of the wiring harness and connectors feeding the valve body, looking for chafed wires, bent pins, corrosion buildup, or unsecured plugs. Check the transmission fluid level on a level surface and inspect its color and smell—dark, burnt-smelling fluid indicates heat damage and internal wear. Finally, use a transmission-capable scan tool to view live solenoid states, input and output speed sensor data, and line pressure readings. After clearing the code, drive the vehicle under conditions matching the freeze frame data and verify that P0C23 does not return.
Repair Options and Costs
Tackle the least expensive and most common problems before committing to major work. Wiring repairs or connector replacement typically run $150–$300 depending on the extent of the damage and whether the harness is serviceable or needs replacement. Replacing a failed shift solenoid costs $300–$800 for parts and labor. A transmission fluid drain-and-fill or flush with filter service runs $150–$350. If the valve body itself is worn, repair or replacement including solenoid pack typically costs $700–$1,500. The most expensive scenario is a full transmission teardown, rebuild, or unit replacement, which ranges from $2,500 to $5,500 depending on the vehicle and whether a new or remanufactured unit is sourced.
Total Repair Cost
P0C23 repair costs vary widely based on the underlying cause. A simple fluid service might be all that is needed for $150–$350, while a failed solenoid adds $300–$800. Valve body work can reach $700–$1,500, and a complete transmission rebuild or replacement may run $2,500–$5,500. Labor rates at independent shops average $80–$120 per hour. Most shops charge a diagnostic fee of $100–$200 to perform the actual testing before quoting repair. Spending that diagnostic dollar upfront prevents buying an expensive part when the real problem is a $20 connector.
Driving Safety Assessment
If the transmission still shifts predictably and no limp mode is active, limited driving at lower speeds to reach a repair facility is acceptable. Avoid sustained highway speeds and aggressive acceleration while the fault is present. If the vehicle exhibits slipping, refuses to move, or is stuck in a single gear, stop driving and arrange a tow. Continued operation in these conditions can destroy clutch packs, score the valve body, or damage the torque converter, turning a $300 solenoid fix into a $5,000 transmission replacement. P0C23 carries a caution severity rating—address it promptly but do not ignore it.