P0B0B — Auxiliary Transmission Fluid Pump Motor Supply Voltage Circuit High

P0B0B — Auxiliary Transmission Fluid Pump Motor Supply Voltage Circuit High. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: wiring or connector faults in the valve body harness, faulty transmission speed sensor, failed shift or pressure control solenoid.

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 P0B0B 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 With the auxiliary transmission fluid pump motor supply voltage disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
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 P0B0B does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0B0B (parts and labor, USD, independent shop rates): Replace a shift solenoid: $300–$800; Valve body repair or replacement: $700–$1,500; Transmission fluid service: $150–$350; Transmission rebuild or replacement: $2,500–$5,500. Overall, fixing P0B0B 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 P0B0B clear itself?

Sometimes P0B0B 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.

How much does it cost to fix P0B0B?

Replace a shift solenoid — $300–$800; Valve body repair or replacement — $700–$1,500; Transmission fluid service — $150–$350; Transmission rebuild or replacement — $2,500–$5,500. 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 P0B0B myself?

Start with a scan: confirm P0B0B, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the auxiliary transmission fluid pump motor supply voltage, and verify the suspect component against live data before buying parts.

Is it safe to drive with P0B0B?

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.

What are the symptoms of P0B0B?

Drivers most often notice: Check Engine or transmission warning light on, slipping between gears, no movement in severe cases, transmission stuck in one gear (limp mode).

When your OBD2 scanner displays P0B0B, the vehicle's control unit has identified a problem with the circuit that supplies voltage to the auxiliary transmission fluid pump motor. The fault description reads "Auxiliary Transmission Fluid Pump Motor Supply Voltage Circuit High," and it falls under the powertrain category since it directly involves the transmission and its electronic controls. This is not a code that triggers on a single bad reading — the module must observe the fault condition recurring under specific operating conditions before it activates the check engine light and stores the code.

To understand why P0B0B sets, you need to know how the affected system works. The auxiliary transmission fluid pump maintains fluid pressure in the transmission, particularly during low-speed or stop-and-go driving when the main pump may not generate sufficient flow. The engine control module monitors the voltage on this pump's supply circuit. When that voltage climbs above the expected range — typically near battery voltage — the module recognizes the circuit is behaving abnormally. This can happen because a signal wire has shorted to a power source, a ground return has opened, or the pump motor itself is pulling the circuit high when it should not be. The freeze frame data stored alongside P0B0B records engine load, RPM, coolant temperature, and vehicle speed at the moment the fault was detected, which gives you a precise starting point for your diagnosis.

P0B0B rarely appears in isolation. In most cases it is the symptom of an underlying problem rather than the root cause itself. Possible culprits range from a straightforward wiring fault to serious internal transmission wear, which is why a systematic approach matters before you spend money on major components.

Symptoms of P0B0B

The warning signs tied to P0B0B reflect how the transmission struggles without proper fluid pump operation. The most obvious indicator is an illuminated check engine or transmission warning light on your dashboard. Beyond that, you may notice the transmission slipping between gears as hydraulic pressure drops. In the worst cases the vehicle loses forward or reverse motion entirely. Many drivers report the transmission entering limp mode, where it locks into a single gear and refuses to shift normally. Shifting may feel harsh or noticeably delayed, and some vehicles shudder or vibrate at highway speeds as the transmission hunts for the correct gear.

Causes of P0B0B

The most frequent cause of P0B0B is a failed auxiliary transmission fluid pump motor that drags the supply voltage circuit high. A signal wire shorted directly to battery positive produces the same result and is relatively common after wiring harness damage. An open ground return on the pump motor circuit can also force the module to read abnormally high voltage. Other potential causes include a faulty transmission speed sensor feeding incorrect data to the control unit, worn clutch plates or torque converter issues, a worn or dirty valve body, low or degraded transmission fluid, and failed shift or pressure control solenoids. Wiring or connector problems in the valve body harness — such as corrosion, broken strands, or loose pins — are also frequent contributors and should not be overlooked.

How to Diagnose P0B0B

Start by connecting an OBD2 scanner and confirming that P0B0B is stored, then capture and save the freeze frame data. This snapshot of engine load, RPM, temperature, and vehicle speed tells you the exact conditions under which the module detected the fault — replicate those conditions during your road test to trigger the issue again. After saving the data, check for any related diagnostic trouble codes. Codes in the same family often point to the real problem faster than the circuit-high code alone. It is also worth searching for manufacturer technical service bulletins specific to your make, model, and model year, since many P0xxx codes have known factory fixes or software calibrations.

Next, perform a thorough visual inspection of the wiring harness and connectors associated with the automatic transmission control. Look for chafed insulation, broken wires hidden under loom tape, corrosion at connector pins, and any signs of water intrusion. With the auxiliary transmission fluid pump motor disconnected from the harness, measure signal voltage at the connector on the vehicle side. A high reading with the motor unplugged confirms a short to power in the harness itself. If the voltage drops to normal the moment you disconnect the motor, the pump motor is the faulty component.

Inspect the transmission fluid level and condition — dark, burnt-smelling fluid is a red flag for internal wear or overheating. Finally, use a capable scanner to read transmission-specific live data: solenoid duty cycles, input and output speed sensor readings, and line pressure values. Once you have verified the repair, clear the code and drive the vehicle through a complete drive cycle that includes the conditions recorded in the freeze frame. Confirm that P0B0B does not return before considering the job complete.

Repair Options and Costs

If the problem originates in the shift or pressure control solenoid, replacing it typically runs between $300 and $800 for parts and labor at an independent shop. A worn or faulty valve body may require repair or full replacement, with costs ranging from $700 to $1,500 depending on whether a remanufactured unit or new part is used. A transmission fluid drain and fill with filter service generally costs $150 to $350, and this should be done regardless of whether it fixes P0B0B, since contaminated fluid accelerates wear throughout the transmission. In severe cases where internal clutches, the torque converter, or the valve body are all compromised, a full transmission rebuild or replacement may be necessary, with total costs between $2,500 and $5,500.

Total Cost to Fix P0B0B

The actual repair cost depends entirely on which component is responsible for the fault. Labor rates at independent shops average $80–$120 per hour in most markets. If a wiring repair or solenoid replacement resolves the issue, you are likely looking at the lower end of the range. If the valve body requires attention, costs climb into the mid-range. The worst-case scenario — transmission teardown or replacement — pushes costs toward $5,500. An accurate diagnosis before purchasing parts is the single most effective way to manage your total expense. Always start with the cheapest and most likely causes: wiring inspection, fluid check, and solenoid testing before committing to major transmission work.

Can You Drive with P0B0B?

This fault warrants caution. If the transmission continues to shift predictably and no warning lights are flashing, short trips on lower-speed roads may be acceptable while you arrange a diagnosis. However, driving at highway speeds with a slipping transmission or a vehicle stuck in limp mode puts additional stress on internal components and can turn a manageable repair into a full transmission replacement. The moment you notice harsh shifting, delayed engagement, or loss of forward motion, the vehicle should be transported to a shop rather than driven.