B1638 — Mirror Driver Right Short To Ground #

Note: The wording of this DTC may vary depending on the vehicle manufacturer.

• B1638 – Passenger Side Mirror Driver Shorted to Ground (Ford)
• B1638 – Right Side Mirror Motor Circuit Short to Ground (Chrysler)
• B1638 – Right Mirror Motor Control Circuit Low (GM)

Summary of Code B1638 #

B1638 is a body system DTC (Diagnostic Trouble Code) that indicates an electrical fault in the passenger-side (right) mirror control circuit. Specifically, it refers to a situation where the driver circuit (the wiring or component controlling mirror movement or defrost/heating) is shorted to ground—meaning the circuit is unintentionally making contact with the vehicle’s chassis ground. This can disrupt normal mirror operation, create further electrical issues, and potentially point to wiring, connector, or mirror motor problems. The code is most commonly found on vehicles equipped with power mirrors and can be triggered by issues ranging from damaged wires to faulty mirror assemblies.

Common Symptoms for Code B1638 #

When B1638 is set, you’ll usually notice one or more direct symptoms affecting your right-side external mirror. Sometimes, the issue can cause other body electronics to behave abnormally, especially if they share wiring harnesses or fuses. Typical signs include:

• Passenger-side (right) mirror not moving or responding to switch input
• Mirror heating/defrost function not working (if equipped)
• Unusual sounds (clicking, buzzing) from the mirror during adjustment attempts
• Blown fuses related to mirror or body electronics
• Warning lights or error messages about mirror function on the dashboard (in some models)

Probable Causes for B1638 (Most to Least Common) #

B1638 is almost always rooted in an electrical issue—but the sources can vary. Here’s a prioritized list of what most often causes this code:

1. Damaged wiring harness (pinched, chafed, or cut wires along the door or mirror harness)
2. Faulty mirror motor (internal short in the right-side mirror assembly)
3. Corroded or loose connectors at the mirror or in the door
4. Short to ground inside the switch (mirror control switch malfunction)
5. Water ingress leading to shorted connections (common after heavy rain or car washing)
6. Defective body control module (BCM) (rare, but possible if all wiring and components check out)

Step-by-Step Diagnostic for Code B1638 #

Accurately diagnosing B1638 means methodically checking the mirror circuit. Here’s a proven technician’s approach:

• Verify the code: Clear the code and see if it returns after operating the mirror.
• Inspect the right mirror and harness: Look for visible damage, pinched wires, or corrosion at connectors.
• Test the mirror motor: With the mirror disconnected, check resistance across motor pins to detect internal shorts.
• Check for ground faults: Using a multimeter, test for continuity between the mirror circuit and chassis ground.
• Examine the control switch: Remove and visually inspect for signs of burning, melting, or internal failures.
• Test connector integrity: Ensure all connectors are fully seated and free of moisture or corrosion.
• Scan for additional codes: Sometimes related codes help pinpoint the root cause.
• If all else passes, test the BCM: Only after wiring, switch, and mirror are ruled out; consult OEM flowcharts for control module testing.

Possible Repairs for B1638 #

Your repair approach should focus on what your diagnosis uncovers. Most fixes are straightforward once the problem’s source is confirmed:

• Repair or replace damaged wiring in the mirror or door harness
• Replace the right-side mirror assembly if the motor or heating element is shorted internally
• Clean or replace corroded connectors as needed
• Replace the mirror control switch if it’s found to be the short’s source
• Seal and protect connections from future moisture ingress
• Replace the BCM only if all other sources are eliminated and the issue persists (rare)

Is It Safe to Drive with Code B1638? #

Yes, but with limitations. Code B1638 does not directly affect engine or critical safety systems, so your vehicle will still operate normally. However, you’ll lose right mirror adjustment and possibly heating/defrost functions. This can be unsafe if you need to reposition your mirror for visibility, especially in adverse weather or while towing. If the blown fuse also affects other body electronics, further inconveniences may arise. If you notice any electrical burning smell, stop and inspect immediately, as shorts can escalate.

Vehicles Most Commonly Affected by B1638 #

While B1638 is a standardized OBD-II body code, it’s most frequently encountered in vehicles with power mirrors and advanced body electronics, especially:

• Ford (F-150, Explorer, Focus, Escape)
• Chrysler/Dodge/Jeep (Grand Cherokee, Charger, 300C, Ram)
• General Motors (Chevy Silverado, GMC Sierra, Cadillac Escalade)
• Some Toyota and Honda models with powered/heated mirrors
• European brands (Mercedes-Benz, BMW) occasionally report similar codes, under different numbers

Common Mistakes & Best Practices for B1638 #

It’s easy to misdiagnose B1638 if you skip steps or rush the process. Here are the most frequent errors and how to avoid them:

• Assuming the switch is always the culprit—wiring faults are more common
• Replacing the entire mirror before checking for simple connector or harness damage
• Overlooking water ingress, especially after detailing or heavy rain
• Not using a multimeter to check for continuity and shorts
• Failing to clear the code after repair and verify functionality

Quick FAQ: Understanding and Fixing B1638 #

Still have questions? Here are answers to the most common queries:

• Q: Can I just disconnect the right mirror to clear the code?
  A: Disconnecting may temporarily clear the code, but the system will detect the open circuit and set a new code for a missing component.
• Q: Is this problem covered under warranty?
  A: If your car is still under the OEM warranty and the issue is not due to physical damage, it’s typically covered—check with your dealer.