OBD Guide
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B166B

Left Trailer Tow Lamp Control Circuit Low

B166B is an OBD-II diagnostic trouble code meaning: Left Trailer Tow Lamp Control Circuit Low. Common causes: broken or damaged wiring harness, oxidation of contacts. Estimated repair cost: $6–56.

Severity
⚠️ Medium
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$6–56 (est.)

Symptoms

  • Incorrect operation of the left trailer lamp
  • No light in the left trailer lamp
  • Dashboard warning

Causes

  • Broken or damaged wiring harness
  • Oxidation of contacts
  • Relay fault
  • Problems with the trailer control module
  • Burnt out lamp

How to Fix

  1. Check the condition of the lamp and replace if necessary
  2. Inspect the wiring harness for damage
  3. Clean contacts from oxides
  4. Check relay and control module
  5. Test the circuit with a multimeter

Related codes

B166AB166C

FAQ

What does the B166B code mean?

B166B is an OBD-II diagnostic trouble code that indicates: Left Trailer Tow Lamp Control Circuit Low

What causes a B166B error code?

The most common causes of B166B include: Broken or damaged wiring harness; Oxidation of contacts; Relay fault; Problems with the trailer control module.

How do I fix a B166B diagnostic trouble code?

To fix B166B: Check the condition of the lamp and replace if necessary. Inspect the wiring harness for damage. Clean contacts from oxides. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B166B?

Limited driving only, diagnose soon

How much does it cost to fix B166B?

The estimated repair cost for B166B is $6–56. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat