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C1278 Toyota Code - Abnormal Change in Output Signal of Rear Speed Sensor Left

Quick Answer

The C1278 diagnostic trouble code (DTC) for Toyota vehicles indicates an abnormal change in the output signal of the rear speed sensor located on the left side of the vehicle. Common causes include Faulty rear speed sensor, Damaged or corroded wiring/connectors leading to the rear speed sensor, Absence of signal due to sensor misalignment or mounting issues. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
C1278 Toyota indicates Abnormal Change in Output Signal of Rear Speed Sensor Left.
Common causes
Common causes include Faulty rear speed sensor, Damaged or corroded wiring/connectors leading to the rear speed sensor, Absence of signal due to sensor misalignment or mounting issues.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 12, 2024
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Code C1278 Toyota Description

The C1278 diagnostic trouble code (DTC) for Toyota vehicles indicates an abnormal change in the output signal of the rear speed sensor located on the left side of the vehicle. The rear speed sensor is a crucial component of the anti-lock braking system (ABS) and traction control system. It is responsible for measuring the speed of the rear wheels and sending this information to the vehicle's electronic control unit (ECU). When the ECU detects an abnormal change in the output signal from the rear speed sensor, it triggers the C1278 code.

OBDII Code C1278 Toyota - Abnormal Change in Output Signal of Rear Speed Sensor Left
C1278 Toyota Code - Abnormal Change in Output Signal of Rear Speed Sensor Left

Common Causes of C1278 Toyota

  1. Faulty rear speed sensor
  2. Damaged or corroded wiring/connectors leading to the rear speed sensor
  3. Absence of signal due to sensor misalignment or mounting issues
  4. Electronic control unit (ECU) malfunction affecting the rear speed sensor
  5. Issues with the tone ring or reluctor ring that the sensor reads from

Symptoms of C1278 Toyota

  1. Illumination of the ABS warning light on the dashboard
  2. Decreased braking performance, especially during hard stops
  3. Unusual noises coming from the rear wheels during braking
  4. Increased stopping distances or difficulty maintaining control during braking
  5. Traction control system malfunctions or reduced stability while driving

How to Fix C1278 Toyota

  1. Begin by conducting a thorough visual inspection of the rear speed sensor, wiring, and connectors for any signs of damage, corrosion, or misalignment.
  2. Use a multimeter to test the rear speed sensor's output signal and compare it to manufacturer specifications to determine if it is functioning correctly.
  3. If the rear speed sensor is faulty, replace it with a new sensor following the manufacturer's guidelines for installation.
  4. Check and repair any damaged wiring or connectors leading to the rear speed sensor.
  5. Clear the DTC using a diagnostic scanner and perform a test drive to ensure the issue has been resolved.

Cost to Fix C1278 Toyota

The cost of repairing the abnormal change in the output signal of the rear speed sensor left (C1278) on a Toyota vehicle can vary depending on the specific cause of the issue and the cost of parts and labor. In general, the cost of replacing a rear speed sensor can range from $100 to $300, while the cost of repairing wiring or connectors may add additional labor charges. Overall, the total repair cost for this issue can range from $150 to $500, including parts and labor.

What does this mean?

Tech Notes for C1278 Toyota

Because the Rear Axle Hub and Bearing Assembly cannot be disassembled, if the Rear Speed Sensor needs replacement, replace the Rear Axle Hub and Bearing Assembly.

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Information for Specific Toyota Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about C1278 Toyota Code

1. What are the common symptoms of OBDII code C1278 in a Toyota related to the abnormal change in output signal of the rear speed sensor left?

- Common symptoms include erratic speedometer readings, ABS warning light illuminated on the dashboard, and possible traction control issues.

2. What could be the potential causes of OBDII code C1278 in a Toyota?

- The code could be triggered by a faulty rear speed sensor on the left side, damaged wiring or connectors, or a malfunction in the ABS control module.

3. How can I diagnose the issue causing OBDII code C1278 in my Toyota?

- Start by inspecting the rear speed sensor on the left side for any visible damage or corrosion. Check the wiring and connectors for any signs of wear or disconnection. Use a diagnostic scanner to retrieve specific error codes and data related to the issue.

4. Can I drive my Toyota with OBDII code C1278 until I can get it repaired?

- It is not recommended to drive the vehicle with this code present, as it may affect the accurate functioning of the ABS system, traction control, and overall vehicle stability.

5. What are the repair options for fixing OBDII code C1278 in a Toyota?

- Repair options include replacing the rear speed sensor on the left side, repairing or replacing damaged wiring or connectors, or addressing any issues with the ABS control module.

6. Are there any DIY tips for resolving OBDII code C1278 in a Toyota?

- DIY tips include checking and cleaning the connectors, inspecting the wiring for any visible damage, and ensuring proper installation of a new rear speed sensor if needed.

7. How much does it typically cost to repair OBDII code C1278 in a Toyota at a dealership or repair shop?

- The cost can vary depending on the specific cause of the issue, but it may range from $100 to $500 or more for parts and labor.

8. Will resetting the OBDII code C1278 in my Toyota make the issue go away permanently?

- Resetting the code may temporarily clear the warning light, but if the underlying issue is not fixed, the code is likely to reappear once the system detects the problem again.

9. Can extreme weather conditions or rough driving terrain trigger OBDII code C1278 in a Toyota?

- Yes, extreme weather conditions or driving on rough terrain can potentially damage the rear speed sensor or wiring, leading to the abnormal output signal detected by the system.

10. How critical is it to address OBDII code C1278 promptly in a Toyota?

- It is crucial to address this code promptly as it directly impacts the functionality of important safety systems like ABS and traction control, which are essential for vehicle stability and braking performance.

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