B2429 — A/C Post Heater Sensor #2 Circuit Short to Ground

What is the most common cause of B2429?

The most common causes are: blown fuse or failed relay, faulty switch, motor or actuator of the affected system, damaged wiring in door jambs or wet areas.

Will B2429 clear itself?

Sometimes B2429 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.

What does OBD2 code B2429 mean?

OBD2 code B2429 flags a problem with the body electrical system (A/C post heater sensor #2 circuit short to ground). The car is usually drivable while you plan the repair. Common culprits: blown fuse or failed relay, faulty switch, motor or actuator of the affected system, damaged wiring in door jambs or wet areas.

Is it safe to drive with B2429?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

What are the symptoms of B2429?

Drivers most often notice: no impact on engine operation in most cases, the affected function (locks, windows, lighting, wipers) works intermittently or not at all, warning light on the dashboard.

Code B2429 flags a hard electrical fault in the climate control system: a short to ground somewhere in the wiring that feeds the A/C post heater sensor number two. The body control module watches this circuit constantly while the engine is running. If the voltage signal from that sensor drops below a threshold that the module considers valid, and if that condition persists across enough drive cycles to rule out a momentary glitch, the module logs B2429 and turns on the check engine or body system warning light.

The post heater sensor monitors temperature conditions in the ductwork downstream of the heater core. When its circuit goes short to ground, the module receives a voltage reading that makes no physical sense, so it sets the code and often switches the affected climate function into a fail-safe mode. Freeze frame data stored alongside B2429 records what the engine was doing—RPM, load, coolant temperature, vehicle speed—when the fault was first detected, which narrows down whether the problem occurs during cold starts, high-speed highway driving, or specific climate control settings.

Symptoms of B2429

• The check engine light or a dedicated HVAC warning indicator illuminates on the instrument cluster.
• The A/C system behaves erratically or defaults to a restricted mode.
• The rear window defroster, heated mirrors, or other tied functions stop working.
• In some vehicles, climate control reverts to manual mode with limited adjustments available.
• Engine performance and drivability remain unaffected—this is purely a body electronics issue.
• The warning light may clear temporarily, then return if the underlying fault is intermittent.

Common Causes

• Wiring damage is the leading cause. Chafing where wires pass through door jambs, corrosion from moisture intrusion, and broken strands inside insulation all create paths to ground that trigger B2429.
• Connector problems at the sensor itself or at the harness junction to the body control module. Pins bent from previous repairs, corrosion buildup, or loose plugs produce the same shorted reading.
• Failed A/C post heater sensor #2. When the internal element shorts, the circuit voltage collapses and the module detects a ground fault immediately.
• Blown fuse or faulty relay protecting that specific sensor circuit. A dead fuse cuts voltage entirely, which can also register as an abnormal condition depending on how the module interprets no signal.
• Body control module malfunction. Less common, but a BCM with internal circuit damage can misread valid sensor signals and generate a false B2429.
• Software calibration gap. Some vehicles released with early TCM or BCM calibrations set this code under normal operation; a dealer reflash corrects it.

How to Diagnose B2429

1. Connect an OBD2 scanner, retrieve B2429, and record the freeze frame data. Note the RPM, load, coolant temperature, and speed recorded when the code first appeared—this tells you which driving scenario triggers the fault.
2. Check for related codes before clearing anything. Codes in the B0xxx or C1xxx ranges often point to the root cause—a failing ground, a module communication issue, or a sister sensor on the same circuit.
3. Inspect the wiring harness physically. Focus on flex points: door hinges, cowl passages, and anywhere the harness bends. Look for cracked insulation, greenish corrosion, or tape that has unraveled. Wiggle connectors while watching live data to spot intermittent drops.
4. Test circuit resistance and ground integrity with a multimeter. At the sensor connector, check that the signal wire shows the correct reference voltage from the BCM, and that neither the signal nor the ground wire reads continuity to chassis ground when they should not.
5. Operate the climate system under load while monitoring the sensor PID in the scanner. If the voltage collapses only when the blower motor runs on high or when defrost is activated, the short is likely heat- or vibration-induced.
6. Clear B2429, complete a full drive cycle that reproduces the freeze frame conditions, and verify the code does not return. Intermittent shorts will often come back within a few cycles.

Repair Options and Costs

Wiring repair or connector service — $80–$250. Most straightforward when the problem is visible corrosion or a crushed wire. Cleaning connector pins, applying dielectric grease, and sealing a chafed harness runs low on parts and moderate on labor.

A/C post heater sensor #2 replacement — $120–$450. The sensor itself is a relatively inexpensive part; the cost skews higher when labor requires disassembling dashboard trim or reaching the ductwork behind the glovebox.

BCM repair or replacement — $300–$900. Full BCM replacement is the costliest scenario and should only be considered after all wiring and sensor tests come back clean.

Total cost for B2429 typically lands between $80 and $900 depending on what is actually failed. The cheapest path is never to assume the BCM is the problem and throw parts at it—start with a thorough visual inspection and multimeter confirmation of the short before committing to major expense.

Can You Drive with B2429?

Generally yes. B2429 is classified as a short driving-safety risk because it does not impair engine function, braking, or steering. The climate control system may operate in a reduced mode or lose certain features, but the vehicle remains mechanically sound and drivable. That said, if the faulty circuit controls rear defrost, heated mirrors, or front defrost in wet or cold weather, reduced visibility is a genuine safety concern. Central locking or security-related body functions affected by the same BCM fault line could also leave a vehicle insecure. For routine commutes on dry roads, most drivers can continue operating the vehicle until a diagnosis and repair are scheduled.

Related OBD2 Codes

• B2400: B2400 — Manufacturer Controlled DTC: Causes, Symptoms & Fix
• B2401: Audio Tape Deck Mechanism Fault
• B2402: Audio CD/DJ Thermal Shutdown Fault
• B2403: Audio CD/DJ Internal Fault
• B2404: Audio Steering Wheel Switch Circuit Fault
• B2405: Audio Single-Disc CD Player Thermal Shutdown Fault