B1740 — Mirror Driver Horizontal Switch Circuit Short To Ground

OBD2 code B1740 flags a problem with the body electrical system (mirror driver horizontal switch circuit short to ground). The car is usually drivable while you plan the repair. Common culprits: damaged wiring in door jambs or wet areas, faulty switch, motor or actuator of the affected system, blown fuse or failed relay.

body electrical

Is it safe to drive?

Short-term driving is OK 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.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1740 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 B0xxx 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 body electrical system for damage, corrosion, chafing or poor contact.
Subsystem check Operate the affected function while watching its switch and motor PIDs in live data.
Subsystem check Inspect connectors and wiring at flex points (door jambs, tailgate hinges) — wires break there first.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1740 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1740 (parts and labor, USD, independent shop rates): Replace the switch or actuator: $120–$450; Repair wiring or connectors: $80–$250; BCM repair or replacement: $300–$900. Overall, fixing B1740 usually costs between $80 and $900. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Is it safe to drive with B1740?

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.

How do I diagnose B1740 myself?

Start with a scan: confirm B1740, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the body electrical system, and verify the suspect component against live data before buying parts.

What are the symptoms of B1740?

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

What does OBD2 code B1740 mean?

Will B1740 clear itself?

Sometimes B1740 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.

The mirror driver horizontal switch circuit short to ground code, B1740, points to an electrical issue within your vehicle's body control network. Specifically, the powertrain or body control module has detected that a signal circuit meant to carry voltage is instead being pulled to ground unexpectedly. This type of fault falls under the body electronics category in the OBD2 standard, which handles everything from door locks and window motors to lighting circuits and wiper systems. When the module sees this abnormal ground condition persist across multiple ignition cycles under specific load conditions, it stores B1740 and illuminates the check engine or body fault light.

Understanding why this code triggers requires knowing how modern body electrical systems work. Switches in these circuits typically ground a signal line when activated, telling the control module you want a particular function to operate. The module then supplies power to the motor or actuator. When B1740 sets, it means the module is reading a grounded condition on that signal line even when the switch isn't being pressed. This isn't a one-time electrical spike—the module requires the condition to repeat before confirming a genuine fault. That's why the freeze frame data stored alongside B1740 is valuable: it captures engine load, RPM, coolant temperature, and vehicle speed at the exact moment the problem occurred, giving you precise conditions to replicate during diagnosis.

Body electrical faults like B1740 rarely affect how your engine runs or your transmission shifts. The powertrain remains untouched by these circuits. However, the systems controlled by the affected switch may stop working or work only intermittently, which can range from a minor annoyance to a safety concern depending on which function fails.

Common symptoms of B1740

Dashboard warning light remains illuminated after the fault is detected
The affected electrical function operates sporadically or fails to respond at all
No change to engine performance, fuel economy, or drivability under normal conditions
Possible complete failure of related systems such as power mirrors, door locks, windows, interior lighting, or windshield wipers
Intermittent operation that comes and goes with temperature changes or vehicle vibration
In some cases, no obvious symptom beyond the stored code and lit warning indicator

What causes B1740?

Blown fuse or faulty relay supplying the affected circuit
Corroded, damaged, or loose electrical connectors in the door jambs or other flex areas
Broken or chafed wiring insulation allowing unintended ground contact
Failed body control module unable to properly interpret switch inputs
Malfunctioning switch, mirror motor, or actuator creating a direct short to ground
Water intrusion in connectors or wiring harnesses, particularly in areas exposed to the elements

How to diagnose B1740

Connect an OBD2 scanner and verify that B1740 is stored in the body control module. Save the freeze frame data before clearing anything—this snapshot tells you engine load, RPM, coolant temperature, and vehicle speed when the fault first appeared.
Check for any related diagnostic trouble codes. Body electrical faults often appear in clusters, and a secondary code might point you directly to the failed component rather than the circuit.
Inspect the wiring harness and connectors associated with the mirror circuit or whatever system B1740 affects on your specific vehicle. Look for frayed wires, corroded pins, broken insulation, and loose or unplugged connections.
Examine the switch itself. The driver-side mirror horizontal switch can fail internally, creating a short that grounds the signal line. Operate the switch while monitoring the circuit with a multimeter or scanner live data to see if the signal behaves correctly.
Pay close attention to flex points where wiring passes through door jambs, hatches, or trunk lids. These areas experience constant flexing and are prone to broken strands inside the insulation, which can cause intermittent ground faults.
Clear B1740 after your inspection and road test the vehicle under the exact conditions recorded in the freeze frame data. If the code returns, you have confirmed an active fault that requires repair.

Repair options with costs

Depending on what your diagnosis uncovers, here are typical repair approaches and what they typically cost at an independent shop:

Switch or actuator replacement: $120–$450. If the mirror switch or motor itself has failed shorted internally, replacing the defective component resolves the issue.
Wiring or connector repair: $80–$250. Broken wires, corroded connectors, or damaged terminals can often be repaired without full harness replacement. Splicing in new wire segments or cleaning/replacing connectors typically falls in this range.
Body control module repair or replacement: $300–$900. When the BCM itself is faulty and causing multiple body electrical codes, it may need to be sent out for repair or replaced with a calibrated unit.

How much does it cost to fix B1740?

Your total repair bill hinges entirely on what component triggered the code. Most B1740 faults trace back to simple issues—bad switches, corroded connectors, or broken wires in the door boot. These repairs sit at the lower end of the scale. BCM replacement becomes necessary only when multiple circuits fail and the module itself is confirmed defective. A reasonable budget expectation for B1740 runs between $80 and $900, with most cases falling well below the upper limit. Spending time on accurate diagnosis before purchasing parts always pays off here—the $20 switch beats the $600 module replacement every time.

Can you drive with B1740?

In most cases, B1740 presents no drivability concern. Your engine will start, accelerate, and stop exactly as it should. The fault lives entirely in the body electrical system. That said, consider which specific function the code affects before dismissing it entirely. If your exterior lighting circuit triggered B1740, driving at night or in poor visibility becomes genuinely hazardous. A failed central locking system can leave your vehicle unsecured. Wiper motor failure during rainstorms creates a safety issue. Use your judgment: a mirror adjustment problem can wait for scheduled service, but a dead horn or broken brake lights warrant immediate attention.