B1738 — Mirror Driver Horizontal Switch Circuit Open

What are the symptoms of B1738?

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

How much does it cost to fix B1738?

Repair wiring or connectors — $80–$250; Replace the switch or actuator — $120–$450; BCM repair or replacement — $300–$900. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will B1738 clear itself?

Sometimes B1738 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 B1738?

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 does OBD2 code B1738 mean?

OBD2 code B1738 flags a problem with the body electrical system (mirror driver horizontal switch circuit open). The car is usually drivable while you plan the repair. Common culprits: corroded or loose connectors, blown fuse or failed relay, damaged wiring in door jambs or wet areas.

Your scan tool just pulled code B1738. What does that mean for your vehicle? Put simply, B1738 indicates a problem with the driver-side mirror's horizontal adjustment circuit — the electrical pathway that carries signals from the mirror switch to the motor has become interrupted. The code lives in the body electrical portion of the OBD2 system, which handles comfort and convenience features rather than engine management.

"Circuit open" means just what it sounds like: somewhere along the route from switch to motor, the path is broken. No current can flow where the module expects it to. This break could be a severed wire, a connector that has backed out or corroded, a blown fuse, or a switch that has failed internally. When the body control module (BCM) detects that its live voltage readings from this circuit fall outside the factory-calibrated range — and it usually checks this repeatedly over multiple drive cycles — it flags the fault and stores B1738. The module also saves a freeze frame alongside the code, capturing engine RPM, load, coolant temperature, and vehicle speed at the exact moment the problem was detected. That snapshot is worth pulling first, because it tells you exactly what conditions triggered the failure and guides your diagnosis from there.

The affected system itself is straightforward: the mirror switch sends a position command to the BCM, which then powers the horizontal motor in the driver mirror. When the circuit is open, that command never reaches the motor, or the motor feedback never returns to the module. Depending on how the failure behaves, you may see complete loss of function or intermittent operation that comes and goes with vibration or temperature changes.

Symptoms of B1738

• The driver mirror will not move left or right, or only moves when the switch is wiggled or pressed hard
• The malfunction may appear only under certain conditions, such as cold weather or after the vehicle warms up
• No effect on engine performance or drivability — the vehicle still runs and drives normally
• A check engine light or body system warning may illuminate on the dashboard
• In some cases, related body functions on the same circuit may also stop working

Common Causes

The most frequent source of B1738 is a simple open circuit somewhere in the mirror adjustment wiring:

• A blown fuse protecting the mirror circuit — this is the easiest and cheapest item to check first
• An electrical connector that is unplugged, has a pin backed out of its housing, or has developed corrosion from moisture exposure
• A broken or frayed wire in the mirror switch harness, especially in areas that flex repeatedly
• An internally failed mirror driver horizontal switch — the switch contacts wear out over time and can develop an open condition
• Wiring damaged by water intrusion, particularly in lower door panels or areas exposed to rain and road salt
• A faulty body control module — less common, but the BCM can fail and stop reading switch inputs correctly
• A related switch, motor, or actuator sharing the same circuit has failed and pulled the circuit open

How to Diagnose B1738

A systematic approach keeps you from replacing good parts:

1. Connect an OBD2 scanner and confirm B1738 is stored in the body control module. Save the freeze frame data before clearing anything — it shows you the exact conditions (RPM, load, temperature, speed) when the fault was recorded.
2. Look for any related trouble codes in the same module. Secondary codes often point to the real root cause rather than the symptom. Check for manufacturer technical service bulletins (TSB) covering your make, model, and year — factory-known issues sometimes have published solutions or software updates.
3. Perform a thorough visual inspection of the wiring and connectors tied to the mirror circuit. Look for chafed insulation, pinched wires, greenish corrosion buildup, or connectors that are not fully seated.
4. Run a continuity test on the entire circuit end-to-end with a multimeter. Gently wiggle the harness during the test — an intermittent open will show up as a reading that jumps or goes OL when the wire is flexed.
5. Monitor the switch and motor signal voltages in the scanner's live data while physically operating the mirror switch. This tells you whether the BCM is receiving the input and sending output to the motor.
6. Pay close attention to flex points: door jambs, tailgate hinges, and any area where wires pass through sheet metal. These are the most common places for broken strands.
7. After repairs are made, clear the code and complete a full drive cycle that reproduces the conditions shown in the freeze frame. Re-scan to confirm B1738 does not return.

Repair Options and Costs

Start with the cheapest possible fixes before moving to expensive components:

• Wiring repair or connector replacement — $80–$250
• Mirror driver horizontal switch replacement — $120–$450
• Body control module (BCM) repair or replacement — $300–$900

How Much Does It Cost to Fix B1738?

Repair cost for B1738 varies based entirely on which part actually failed. Here are typical scenarios using independent shop labor rates in the United States:

• Wiring repair or connector replacement: $80–$250
• Switch or actuator replacement: $120–$450
• BCM repair or replacement: $300–$900

Across all scenarios, fixing B1738 generally runs between $80 and $900. The wide range reflects how many different components can cause an open circuit. A proper diagnosis before buying any parts is the single best way to keep total cost down — the BCM replacement scenario is the most expensive option and should be your last resort, not your first assumption.

Can You Drive with B1738?

B1738 is classified as short severity — the fault does not impair the engine, transmission, brakes, or safety restraints. In most vehicles, you can continue driving without concern for drivability. The mirror horizontal adjustment is a convenience feature, not a safety-critical system. However, there are a couple of exceptions worth noting: if the open circuit affects exterior lighting or the windshield wipers, you lose important visibility aids. Some central locking faults stored under body codes can leave the vehicle unsecured. Aside from those edge cases,