C1402 – Malfunction in Front Speed Sensor LH Circuit


By Reinier (Contact Me)
Last Updated 2016-10-27
Automobile Repair Shop Owner

CodeFault LocationProbable Cause
C1402 Malfunction in Front Speed Sensor LH Circuit (Most Manufacturers)
Traction Control Valve RF Circuit Short To Ground
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What Does Code C1402 Mean?

SPECIAL NOTES: Although many resources and most generic code readers display the definition of manufacturer-specific OBD II code C1402 as “Traction Control Valve RF Circuit Short To Ground”, it should be noted that this definition is not in current use in the US domestic market. For reasons that are mostly technical in nature, many manufacturers in the US market define code C1402 as “Malfunction in Front Speed Sensor LH Circuit”, which definition describes a fault in a system that directly affects three safety-critical systems- the affected systems being the ABS, Traction Control, and Stability Control systems.

Being a manufacturer-specific code, carmakers are largely free to assign their own definitions and descriptions to C1402, or any other code that does not have a “0” as the second character. Refer to the Related Codes section of this guide for some examples of definitions of code P1402 other than “Malfunction in Front Speed Sensor LH Circuit”.

Always refer to the manual for the application being worked on for detailed information on how code P1402 is defined for that particular application, which could be different from how it is defined for other applications in any given model range. END OF SPECIAL NOTES.  

OBD II fault code C1402 is a manufacturer specific code that many manufacturers define as “Malfunction in Front Speed Sensor LH Circuit”, and which is set when the PCM (Powertrain Control Module), or other controller such as the ABS, Traction Control, and/or the Stability Control Module detects a malfunction in the circuit that monitors the wheel speed sensor of the left-hand front wheel.

When diagnosing code C1402, it is important to recognize that wheel speed sensors (both singly and collectively), supply the reference data for the extremely complex algorithms that control the ABS, Traction-, and Stability Control systems. All three of these systems are safety-critical, and a malfunction in any wheel speed sensor’s control/monitoring circuit could result in the partial or complete loss of functionality in one or more of these systems, a circumstance that could have serious, if not fatal results for a vehicles’ occupants.

In terms of operating principles, a wheel speed sensor consists of two parts; a sensor, which could be either an “active” (Hall Effect), or a “passive” (magnetic) sensor, and a device called a “reluctor ring” (also sometimes referred to as a “tone ring”, or less often, a “toothed wheel”. In a fully functioning system, both types of sensor generate a signal voltage when the “teeth” of the reluctor ring pass in front of the sensing element, with the gap between the teeth of the reluctor ring causing the signal voltage to reduce, or fall away. Thus, as the reluctor ring rotates, the signal voltage switches from high-to-low-to-high, which switching forms the basis upon which one or more control modules calculate the rate of rotation of each wheel.

In practice, the speed at which each wheel rotates is fed to the ABS control module via a dedicated circuit, to be shared with the Traction Control -, Stability Control -, and Powertrain Control modules via the CAN (Controller Area Network) bus system. At this point, it should be remembered that the ABS system is the foundation upon which both the Traction -, and Stability Control systems depend for their “operating instructions”.

Both systems share many of the ABS systems’ components, but it is the ABS system that supplies (via its control module) the selective braking forces to individual wheels to correct wheel spin during acceleration, as well as selective braking forces to individual wheels to force the vehicle into following the steering angle set by the steering angle sensor when a potentially dangerous situation is detected by the Stability Control system

However, since all of the above functions depend on the actual, and accurate rate of rotation of each wheel being relayed to the relevant control modules, none of these functions may be available to the driver should a malfunction exist in the control/monitoring circuit(s) of any wheel speed sensor.

The image below shows the typical location of a Hall Effect wheel speed sensor relative to other axle components. Note however that the design and location of wheel speed sensors vary between applications: in the case of magnetic sensors, the reluctor wheel is often located inside the wheel bearing.



What are the common causes of code C1402?

The possible causes of code C1402 are much the same across applications, regardless of the type of wheel speed sensor fitted to the vehicle. Nonetheless, even though the possible causes might be similar, the causes that affect Hall Effect sensors are different from those that affect magnetic sensors. Below are some possible causes of code C1402 on applications with Hall Effect sensors-

  • Compromised winding efficiency. (Common on substandard aftermarket sensors)
  • Insufficient number of windings on the coil. (Common on aftermarket sensors)
  • Size and strength of the magnetic core. (Common on substandard aftermarket sensors)
  • Reluctor ring may be damaged, clogged, or absent.
  • Total system resistance may exceed allowable values.

Below are some common causes of code P1402 on applications that use magnetic sensors-

  • Insufficient or excessive air gap between the sensor tip and the reluctor ring. Although this is becoming a rare event, there are still some applications on which the air gap can be adjusted.
  • Fractured permanent magnet in the sensor.
  • Damaged, worn, or maladjusted wheel bearing(s).
  • Reluctor ring damaged, clogged, or absent.
  • Wheel bearing installed incorrectly. In some cases, the reluctor ring in the bearing is located on one side of the bearing. Installing the bearing incorrectly therefore places the reluctor out of the sensors effective range.

The following possible causes are common to both types of sensors-

  • Damaged, burnt, shorted, disconnected, and/or corroded wiring and/or connectors
  • Poor or incorrect sensor installation.
  • Control module failure. This is not altogether impossible, but determining in what respect a control module is defective is best left to professional technicians.
  • Incorrectly programmed control modules. This is a rare event that requires professional grade equipment to identify.

What are the symptoms of code C1402?

Apart from a stored trouble code and an illuminated warning light, the possible symptoms of code C1402 are largely make and model specific. Depending on the model and the exact nature of the problem, some, or all functionality from one or more of the systems that depend on the wheel speed sensors for input data may be lost. Refer to the relevant manual for the application being worked on for detailed information on possible symptoms that may be present on that particular application.

How do you troubleshoot code C1402?

NOTE #1: Where code C1402 is used with the definition “Malfunction in Front Speed Sensor LH Circuit”, it is generally safe to assume that the malfunction is located either in the wheel speed sensor on the left front wheel itself, or in the wiring between the sensor and the relevant control module. However, while control module failure is not altogether impossible, it is a rare event and the fault must be sought elsewhere before any controller is replaced.

NOTE #2: While it is possible to diagnose and repair malfunctions in wheel speed sensors by using “generic” methods, non-professional mechanics are nevertheless strongly urged to obtain an official ABS/Traction Control/Stability Control system diagnostic flow chart for the particular application being worked on. Since the setting parameters for this code vary between applications, official diagnostic flow charts usually cover all the possible bases, so to speak, meaning that all code setting parameters, as well as all possible checks and tests for that particular application are included.

NOTE #3:  It should be noted that “malfunction” in this context can include deviations in the waveform produced by the sensor, which are different for the two types of sensors in use. Hall Effect sensors produce a square waveform, while magnetic sensors produce a deep sine wave, but both waveforms can be affected by defects in the reluctor ring in much the same way. The image below shows the typical deviations from a steady waveform that can be caused by damaged reluctor rings.


This type of problem can only be diagnosed with a laboratory-grade oscilloscope, meaning that if the code persists despite having performed “standard” checks and an oscilloscope is not available, the better option is to refer the vehicle for professional diagnosis and repair, since the types of damage to a reluctor ring that can influence a waveform is not always readily apparent, and especially if the reluctor ring is located inside the wheel bearing.

NOTE #4: Be aware that the diagnostic/repair steps outlined here are generic in nature, and as such, they may or may not serve to resolve this code. Always refer to the manual for the application being worked on for detailed information on possible diagnostic/repair procedures that apply to that particular application.

Step 1

Assuming that a diagnostic flow chart is not available, record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

Step 2

Consult the manual to determine which type of wheel speed sensors are present on the application, but be aware that manuals are not always accurate on this point, since manufacturers sometimes change sensors and other equipment without updating the repair manual.

NOTE #1: Hall Effect sensors have three wires; one wire carries a reference voltage (usually 12 VDC) since this type of sensor cannot generate a current on its own, one other wire carries the generated AC signal voltage to one or more control modules, while the remaining wire is a ground.

NOTE #2:  Magnetic sensors only have two wires; one that carries the generated signal voltage, and a ground.

Step 3

Consult the manual to locate the affected wheel speed sensor. Note that in most cases, removing the wheel is required to gain unimpeded access to the sensor. If the sensor has only two wires, it is a passive, magnetic sensor that can be influenced by worn, damaged, or maladjusted wheel bearings.

Consult the manual on the correct procedure to check the wheel bearing for free play or damage. If the bearing is worn, damaged, or not adjusted correctly, there is no point in further diagnosing the code before correcting the problem with the wheel bearing. Note that in some cases, code P1402 can be resolved by replacing the bearing.

NOTE: While it is possible to replace a wheel bearing on its own, it is always better to replace the entire hub that incorporates the bearing, since this eliminates the possibility of causing damage to the bearing during the replacement process. Also, be aware that replacing a wheel hub requires a moderate degree of mechanical aptitude, as well as tools that may not always be ready at hand. If the required tools and equipment are not available, refer the vehicle to repair shop to have the hub replaced professionally.

Step 4

If the wheel bearing is sound, inspect the sensor and its surrounds for the presence of mud, dirt, or other accumulations that could possibly clog the teeth of the reluctor wheel. If such deposits and accumulations are found, consult the manual on the correct procedure to remove the sensor so that the offending matter can be removed. Once all accumulated mud or other gunk is removed, refit the sensor, and test the working of the sensor in accordance with the instructions in the manual to see if the code returns.

NOTE: With the sensor removed, inspect it (and is wiring) for signs of damage to the sensor and/or the wiring. Look for damaged, burnt, shorted, or corroded wiring and/or connectors. Replace the sensor if it or the wiring is visibly damaged in any way. Note that the wiring leading away from the sensor cannot be repaired, since it is shielded to suppress radio interference.

Step 5

If the code persists, but there is no visible damage to the wiring, prepare to perform resistance, continuity, ground, and reference voltage checks on all associated wiring.

NOTE: Hall Effect sensors have three wires; one wire carries a reference voltage since this type of sensor cannot generate a current on its own, one other wire carries the generated signal voltage to one or more control modules, while the remaining wire is a ground.

Consult the manual to determine the function of each wire, but be sure to disconnect the sensor from all control modules to prevent damage to the controller, but also to be sure that you are testing only the sensor and its wiring. Consult the manual on the correct testing procedure(s) for that particular type of sensor; compare all obtained readings with those stated in the manual, and replace the sensor if discrepancies are found.

NOTE: The wires leading out of a magnetic sensor are usually twisted together to suppress electronic noise. Disturbing or interrupting this twist can set a malfunction code. Nine times out of ten, the malfunctions associated with code C1402 are caused by damage either to the sensor itself, or with the wiring leading away from it. Damage is typically caused by accumulations of dirt, mud, or slush from salt-treated roads, water intrusion, or impacts by road debris.

Step 6

Due to their location, wheel speed sensors are subject to harsh conditions that can cause types of damage that are not always visible or apparent. Therefore, it should not be assumed that the wiring is fine when tests do not reveal trouble the first time round, so perform the following two tests as well-

The Wiggle Test:

As the name suggests, wiggling the wiring at the sensor or on either side of the connector can reveal intermittent contact issues. Thus, when performing resistance, ground, reference voltage, or continuity checks, wiggle the wires a bit to see if any reading changes while the wiring is being wiggled about. Replace the sensor and all affected wiring if the wiggle test reveals changes in readings that should be constant.

The Saltwater Test:

Since saltwater conducts electricity better than pure water does, add some salt to water to produce a 5% saline solution, and spray this solution onto the sensor, wiring, and connector with a spray bottle. If any part of the system leaks to ground or power, the salt solution is almost certain to cause a short circuit that will be revealed during testing. If such a short circuit reveals itself, replace the sensor and all suspect wiring, clear all codes, and retest the system in accordance with the instructions in the manual to see if the code returns.

NOTE: Simply spinning the wheel by hand to check for the presence of a signal voltage does not work, and it is not a recommended diagnostic method. All systems, regardless of the type of sensor present, require the wheel to spin at a very specific speed (consult the manual on this point) before one or more automatic self-tests can run successfully. The only other way to test the working of a wheel speed sensor is drive the vehicle at the recommended speed with an oscilloscope attached, which is not a practical test to run for the vast majority of DIY mechanics.

Step 7

If the wiring checks out OK, the wheel bearing is sound, and the sensor/reluctor ring is clean and free of gunk but the code persists, it is likely that the reluctor ring has suffered some sort of damage. Be aware that this is not always easy to check or verify since in many, if not most cases, the reluctor ring is not clearly visible or accessible without first having to disassemble the hub/axle.

If the reluctor ring is suspected to be cause of the problem but the reluctor ring is located in the wheel bearing, the wiser option is to refer the vehicle for professional diagnosis and repair. This is also true if the reluctor ring is located outside of the bearing, since some disassembly of the axle is often required to gain access to it.

NOTE: While it is certainly possible to disassemble a hub to gain access to the reluctor ring on a DIY basis, doing so often requires skills and tools/equipment the average DIY mechanic does not possess, or have access to.

Step 8

WARNING: Non-professional mechanics are strongly urged NOT to continue the diagnostic process beyond Step 7 if the generic test methods outlined up to this point had not resolved code C1402. From this point onward, it is likely that one or more control modules and/or some parts of the Can bus system may be implicated, which is an area of automotive diagnostics that is best is left to expert technicians. Diagnosing faults in the CAN bus system requires professional-grade equipment, above average diagnostic skills in general and expert level knowledge of the application in particular.

Therefore, if the fault persists beyond Step 7, refer the vehicle for professional diagnosis and repair to avoid the distinct possibility of inadvertently causing fatal damage to the vehicles’ electrical system.

Codes Related to C1402

Note that the related codes listed below ONLY apply to applications where code C1402 is defined as “Malfunction in Front Speed Sensor LH Circuit”.  

  • C1401 – Relates to “Malfunction in Front Speed Sensor RH Circuit”
  • C1403 – Relates to “Malfunction in Rear Speed Sensor RH Circuit”
  • C1404 – Relates to “Malfunction in Rear Speed Sensor LH Circuit”

NOTE: Be aware that there are other definitions for code C1402, even within the USDM. Below are some examples but take note that the list of examples presented here is likely not exhaustive, nor complete. Always consult the manual for the application being worked on for detailed information on the exact definition of C1402 as it relates to that particular application.

  • Chrysler/ Dodge/Jeep – Transfer Case Range Select Switch Circuit High
  • Ford/Lincoln/Mercury – Right Front Traction Assist Valve coil short circuit to battery
  • Mazda – Right Front Traction Assist Valve coil short circuit to battery