B1748 — Mirror Passenger Horizontal Switch Circuit Short To Ground

B1748 — Mirror Passenger Horizontal Switch Circuit Short To Ground. A fault in the body electrical system. The car is usually drivable while you plan the repair. Typical causes: body control module (BCM) fault, corroded or loose connectors, damaged wiring in door jambs or wet areas.

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 B1748 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 B1748 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1748 (parts and labor, USD, independent shop rates): BCM repair or replacement: $300–$900; Replace the switch or actuator: $120–$450; Repair wiring or connectors: $80–$250. Overall, fixing B1748 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

What are the symptoms of B1748?

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

What does OBD2 code B1748 mean?

How much does it cost to fix B1748?

BCM repair or replacement — $300–$900; Replace the switch or actuator — $120–$450; Repair wiring or connectors — $80–$250. 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 B1748 myself?

Start with a scan: confirm B1748, 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 is the most common cause of B1748?

The most common causes are: body control module (BCM) fault, corroded or loose connectors, damaged wiring in door jambs or wet areas.

B1748 indicates a fault in the electrical system responsible for adjusting your passenger-side mirror horizontally. The code specifically points to a short-to-ground condition in the switch circuit — meaning an unintended connection has formed between the mirror adjustment wiring and the vehicle's metal frame. When the body control module detects this abnormal electrical path, it logs B1748 after confirming the condition across multiple ignition cycles.

Your vehicle's BCM constantly monitors the voltage in the mirror switch circuit using internal sensors. Under normal circumstances, the module expects to see specific voltage ranges when you operate the switch. When a ground short develops, the voltage drops unexpectedly, triggering the fault detection logic. The module also stores a freeze frame snapshot alongside B1748 — capturing engine rpm, load, coolant temperature, and vehicle speed at the exact moment the problem was detected. That snapshot is invaluable during diagnosis because it tells you what conditions were present when the failure occurred.

Common Symptoms of B1748

The passenger mirror fails to adjust horizontally or responds only intermittently
The mirror switch may feel warm to the touch or stop responding entirely
Other body electrical functions (windows, locks, lighting) may operate unpredictably depending on circuit design
An illuminated warning light appears on the instrument cluster
The affected circuit may stop working completely until the short is resolved
In rare cases, the BCM disables the circuit temporarily to prevent further electrical damage

Typical Causes of B1748

Faulty mirror switch — internal contacts can short internally, creating an unwanted ground path; this is the most frequent culprit
Damaged wiring in the door jamb — flexing wires and exposure to moisture commonly cause insulation breakdown at hinge points
Corroded or loose connectors — moisture intrusion at electrical junctions creates resistance and intermittent shorts
Body control module failure — less common but possible if the module itself sustains internal damage from the electrical fault
Blown fuse or failed relay — protective devices may have operated correctly to prevent worse damage
Chafed wiring in wet areas — water and road salt accelerate insulation degradation, especially along door edges

How to Diagnose B1748

Connect an OBD2 scanner and confirm B1748 is stored in the body control module. Record the freeze frame data — this shows engine conditions when the fault was detected and helps you replicate the failure scenario.
Check for related trouble codes. Body electrical problems often appear in groups, and addressing all of them simultaneously prevents repeat repairs. Search the manufacturer database for technical service bulletins covering B1748 on your specific model year.
Visually inspect the door wiring boot at the passenger mirror. This is the most vulnerable location — wires flex every time the door opens and moisture collects here. Look for cracked insulation, green corrosion, or broken strands.
Test the mirror switch with a multimeter according to the service manual specifications. A shorted switch typically shows near-zero resistance between terminals that should be isolated from ground.
Wiggle-test the wiring harness while monitoring live data from the mirror motor. Any interruption or short condition that appears during flexing confirms a wiring fault at that location.
Clear B1748, then operate the mirror switch through its full range during a test drive. If the code returns, you have confirmed a hard failure rather than an intermittent condition.

Repair Options and Expected Costs

Replacing the faulty mirror switch is the most straightforward and frequently successful repair. Switches for passenger-side mirrors typically run between $120 and $450 depending on your vehicle make and whether you use OEM or aftermarket parts. Labor adds little time to this job since the switch is usually accessible from inside the door panel.

If the problem lies in the wiring or connectors, expect to pay $80 to $250 for the repair. Most wiring issues in the door jamb can be spliced and sealed, though some technicians recommend replacing the entire harness segment to prevent future failures.

Replacing the body control module itself is the most expensive scenario, ranging from $300 to $900. The BCM requires programming to match your vehicle, and this work is best left to a dealer or qualified specialist.

Driving Safety Verdict

B1748 carries a short severity rating — the mirror adjustment fault poses no direct threat to engine operation or braking systems. You can continue driving with reasonable caution, adjusting your driving habits to compensate for reduced rear visibility from the affected mirror. However, if the underlying short begins affecting other body electrical functions or triggers cascading BCM faults, have the vehicle inspected before longer trips. The repair is rarely urgent from a safety standpoint, but leaving the circuit shorted risks eventual damage to other components.