P0C29 – Drive Motor “B” Torque Control

P0C29 is a hybrid/EV trouble code that can be a little intimidating when you first see it on your scan tool, especially if you’re not used to high-voltage systems. This code points to a problem in the battery pack or its monitoring circuit, and it should never be ignored. In this guide, you’ll learn what P0C29 means in plain language, the most common causes, what symptoms to watch for, and how a technician would diagnose and repair it. That way, you can talk to your shop confidently or decide what you can safely check yourself.

What Does P0C29 Mean?

P0C29 is an OBD-II generic hybrid/EV diagnostic trouble code that typically translates to a high-voltage battery or battery module performance issue. The exact wording varies by manufacturer, but it usually indicates that the hybrid battery control module (or battery ECU) has detected an abnormal voltage, resistance, or temperature condition in one part of the battery pack.

In simple terms, the computer is seeing one section of the high-voltage battery behaving differently from the others. When the readings fall outside the expected range for a set period of time, the ECU stores P0C29 and may limit hybrid or EV operation to protect the system.

Quick Reference

• Code: P0C29
• Type: Hybrid/EV high-voltage battery performance fault
• Severity: Moderate to high – can limit hybrid assist or EV mode
• Common symptoms: Reduced power, poor fuel economy, warning lights
• Typical causes: Weak battery module, wiring/connector issues, sensor faults

Real-World Example / Field Notes

In the shop, I usually see P0C29 on higher-mileage hybrids or plug-in hybrids that have spent years in hot climates or heavy stop-and-go traffic. A typical case: a customer comes in with the check engine light, hybrid system warning, and a complaint that the car feels sluggish and the engine runs more than usual. Scanning shows P0C29 plus a specific battery block imbalance code. After checking live data and doing a load test, one or two modules in the pack show lower voltage under load. In those cases, the fix is often replacing the affected modules or, more commonly, replacing or refurbishing the entire high-voltage battery pack.

Symptoms of P0C29

• Warning lights – Check Engine, hybrid system warning, or EV system light illuminated.
• Reduced power – Noticeable loss of acceleration, especially from a stop or when merging.
• Engine running more – Gas engine stays on more often, even at low speeds or light loads.
• Poor fuel economy – Drop in MPG because the hybrid assist is limited or disabled.
• Limited EV mode – EV-only operation may be restricted or disabled completely.
• Battery gauge fluctuations – State-of-charge display jumps up and down abnormally.
• Cooling fan noise – High-voltage battery cooling fan runs more frequently or at high speed.
• Possible fail-safe mode – Vehicle may enter a reduced-power or “limp” mode to protect components.

Common Causes of P0C29

Most Common Causes

• Degraded battery modules – One or more high-voltage battery modules have aged, lost capacity, or developed high internal resistance, causing voltage imbalance under load.
• Battery block imbalance – The battery ECU detects that one block’s voltage is significantly different from the others, triggering P0C29 and related codes.
• High-resistance connections – Corroded or loose bus bars, terminals, or connectors inside the battery pack create resistance and abnormal voltage drops.
• Battery temperature issues – Overheating or uneven temperature across modules due to a weak cooling fan, clogged ducts, or sensor faults.
• Battery ECU logic detecting performance loss – The control module sees that the pack cannot deliver or accept current as expected during charge/discharge events.

Less Common Causes

• Faulty voltage or temperature sensors – A bad sensor or harness can send incorrect data, making the ECU think the battery is failing when it is not.
• Damaged wiring harness – Chafed, pinched, or rodent-damaged wiring between the battery pack, battery ECU, and main hybrid ECU.
• Battery cooling system faults – Failed cooling fan, blocked air intake, or damaged ducting causing localized overheating.
• Previous improper repairs – Poor-quality module replacements, mixed-age modules, or contaminated bus bars from earlier work.
• ECU software issues – Rare, but sometimes a control module software update is needed to refine battery monitoring thresholds.

Diagnosis: Step-by-Step Guide

You’ll want at least a capable scan tool that can access the hybrid/EV system, a digital multimeter, and ideally a battery-safe insulation tester. For anything involving opening the high-voltage battery pack, high-voltage safety gear (insulated gloves, face shield) and proper training are mandatory. If you’re not experienced with HV systems, limit yourself to external checks and let a qualified hybrid technician handle the rest.

1. Confirm the code and record freeze frame data. Connect a scan tool, confirm P0C29, and note freeze frame data (battery SOC, temperatures, voltages, vehicle speed). Check for related battery or hybrid system codes.
2. Check for related DTCs. Look for specific battery block codes (like P0A80-series or P0C3x block codes) that point to a particular module or section of the pack.
3. Inspect battery cooling system. Verify that the battery cooling fan operates, vents are clear, and there’s no debris blocking air inlets. Overheating can trigger or worsen P0C29.
4. View live data for battery blocks. In the scan tool, monitor individual block voltages and temperatures at idle and under light load. Look for any block that consistently reads lower or higher than the others.
5. Perform a controlled load test. With a helper driving (or using a dyno where available), watch how block voltages behave during acceleration and regenerative braking. Weak modules will show greater voltage sag under load.
6. Inspect connectors and bus bars (qualified tech only). With the HV system powered down and the service plug removed, a trained technician can open the battery case to inspect for corrosion, loose bus bars, or burnt connections.
7. Check sensor and harness integrity. Use wiring diagrams to verify continuity and resistance of voltage sense and temperature sensor circuits between the pack and the battery ECU.
8. Review Mode $06 data. On some vehicles, Mode $06 can show battery block test results and margins, helping confirm marginal sections before they fully fail.
9. Evaluate overall battery health. Based on mileage, age, and test results, decide whether it makes sense to replace individual modules, a section, or the entire battery pack.
10. Clear codes and road test. After repairs, clear P0C29 and any related codes, then road test while monitoring live data to confirm the battery pack now stays within normal parameters.

Pro tip: When one module in an older pack fails, others are often not far behind. Replacing the entire pack or using a professionally remanufactured pack is usually more reliable than chasing one weak module at a time.

Possible Fixes & Repair Costs

The exact repair for P0C29 depends on what testing reveals, but most solutions center around restoring proper battery pack performance and reliable sensor data.

• Clean/repair battery cooling system – Clearing vents, fixing ducting, or replacing a weak cooling fan.
• Repair wiring or connectors – Fixing or replacing damaged harnesses, corroded terminals, or loose bus bars.
• Replace faulty sensors – Voltage sense lines, temperature sensors, or the battery ECU if it’s not reading correctly.
• Replace weak battery modules – Swapping individual modules or blocks that show low capacity or abnormal voltage behavior.
• Replace or remanufacture the HV battery pack – The most complete and long-term solution when the pack is generally worn out.

Typical repair costs for P0C29 vary widely. Minor issues like cleaning vents or repairing wiring can run $150–$400. Replacing a cooling fan or sensors might be $300–$800. Replacing individual modules or a reconditioned pack often falls in the $900–$2,000 range, while a brand-new OEM high-voltage battery can run $2,000–$4,500+ installed, depending on make, model, and warranty coverage. Labor rates, parts availability, and whether you choose new vs. remanufactured components all affect the final cost.

Can I Still Drive With P0C29?

In many cases, you can still drive with P0C29 stored, but the vehicle may limit hybrid assist, EV mode, or overall power. The engine may run more often, and you’ll likely see reduced fuel economy. While it might not strand you immediately, you’re driving with a compromised high-voltage system. If the problem worsens, the car can enter a more aggressive fail-safe mode or even refuse to start. It’s best to have the code diagnosed and addressed as soon as possible rather than waiting for a breakdown.

What Happens If You Ignore P0C29?

Ignoring P0C29 can lead to progressive battery damage, overheating, and increased stress on the remaining healthy modules. Over time, that can turn a minor imbalance into a complete battery failure. You also risk the vehicle going into limp mode at an inconvenient time, plus long-term overuse of the gasoline engine, which hurts fuel economy and may create additional wear and emissions issues.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0C29

P0C29 shows up most often on hybrid and plug-in hybrid models from major manufacturers. You’ll commonly see it on Toyota and Lexus hybrids (Prius, Camry Hybrid, Highlander Hybrid, RX, etc.), as well as Honda (Accord Hybrid, Insight), Ford (Fusion Hybrid, C-Max, Escape Hybrid), and GM models (Chevy Volt, Malibu Hybrid). Some Nissan, Hyundai, and Kia hybrids and EVs can also log this code. It tends to appear on vehicles with higher mileage, older battery packs, or those used in hot climates or heavy stop-and-go driving.