If your Honda’s check engine light is on and the scanner shows code P1399, you’re likely looking for a clear explanation. The P1399 Honda code definition points to an issue within the Vehicle Stability Assist (VSA) system, specifically related to the wheel speed sensor circuit or its communication.
This code can be confusing because it involves the stability control system, not just the engine. It means the Engine Control Module (ECM) has detected an irregular signal or a problem in the data coming from the VSA module regarding wheel speed. Your car’s computer uses this data for stability and traction control, and when it’s faulty, it triggers this alert.
P1399 Honda Code Definition
In technical terms, Diagnostic Trouble Code (DTC) P1399 is defined as “VSA Wheel Speed Sensor Circuit Malfunction.” It’s a manufacturer-specific code for Honda and Acura vehicles. The code is set when the Engine Control Module (ECM) receives an implausible or erratic signal from the Vehicle Stability Assist module about one or more wheel speed sensors.
Think of it as a communication breakdown. The wheel speed sensors report how fast each wheel is turning. The VSA module collects this data and sends a summary to the ECM. If the ECM finds this data illogical or missing, it logs P1399 to warn you the stability system may not function correctly.
Common Symptoms of a P1399 Code
You might notice more than just the check engine light. Here are the typical signs:
* Illuminated Check Engine Light: This is always the first indicator.
* VSA/ABS Warning Lights: Often, the VSA warning light and sometimes the ABS light will also illuminate on your dashboard.
* Loss of VSA Function: Your Vehicle Stability Assist system will be disabled. You may see a “VSA System Problem” or similar message on your multi-information display.
* Traction Control Inactive: The traction control feature, which is part of the VSA system, will not work.
* Possible ABS Deactivation: In some cases, the Anti-lock Braking System might also be turned off as a safety precaution.
* No Drivability Issues: Importantly, the car will usually drive normally. You might not feel any difference in acceleration or general driving, but you’ll lack the electronic stability aids.
Primary Causes of the P1399 Code
Pinpointing the cause requires some diagnosis, as it can stem from several areas. Here are the most common culprits, starting with the simplest.
Faulty or Dirty Wheel Speed Sensor
This is a very frequent cause. Each wheel has a sensor that reads a toothed ring (tone ring) on the axle or hub. If one sensor gets dirty, damaged, or fails internally, it sends bad data.
* Dirt and Debris: Metal shavings or road grime can cling to the sensor’s magnetic tip.
* Physical Damage: The sensor can be cracked or broken from road hazards.
* Internal Failure: The sensor’s internal coil or circuitry can wear out over time.
Damaged Tone Ring (Reluctor Ring)
The wheel speed sensor reads the teeth on this ring. If it’s damaged, the signal will be wrong.
* Cracked or Missing Teeth: This causes gaps in the signal.
* Corrosion or Rust Buildup: Heavy corrosion can obscure the teeth.
* Bent Ring: Impact from a pothole or curb can bend the ring out of alignment.
Problems with Wiring or Connectors
The electrical path from the sensor to the module is long and exposed. Issues here are common.
* Chafed or Cut Wires: Wires near the wheel can rub against suspension parts and get damaged.
* Loose or Corroded Connectors: The plugs at the sensor or module can become loose, dirty, or green with corrosion.
* Poor Electrical Connection: A weak connection creates resistance and a faulty signal.
VSA Module or ECM Issues
While less common, the computer modules themselves can be the source.
* VSA Module Malfunction: The module that processes all the wheel speed data could have an internal fault.
* ECM Communication Error: The problem might be in how the ECM receives the data, not necessarily the data itself.
* Software Glitch: Occasionally, a simple software anomaly can trigger the code.
How to Diagnose and Fix P1399
Fixing a P1399 code involves systematic troubleshooting. Always start with the simplest, least expensive possibilities first. You’ll need a basic OBD-II scanner and a digital multimeter for most checks.
Step 1: Scan and Record Codes
Use your scanner to confirm P1399 is present. Also, check for any additional codes. Codes like Cxxxx (ABS/VSA related) can point you directly to a specific wheel. Clear the codes and take the car for a short drive to see if P1399 returns immediately or if other codes appear.
Step 2: Perform a Visual Inspection
This is a crucial and often overlooked step.
* Check each wheel speed sensor. Look for obvious physical damage, dirt caked on the tip, or loose mounting.
* Inspect the wiring harness leading to each sensor. Look for cuts, abrasions, or melted sections.
* Examine the connectors. Unplug them (with battery disconnected) and check for corrosion or bent pins.
* Look at the tone rings. You may need to remove the brake rotor or hub to see them clearly. Check for cracked, missing, or clogged teeth.
Step 3: Test Wheel Speed Sensor Resistance
Use a multimeter set to ohms (Ω). Unplug the sensor and measure resistance across its two terminals. Consult your vehicle’s service manual for the exact specification, but it’s typically between 800 and 2500 ohms. Also check for infinite resistance (open) or zero resistance (short). Compare readings from all four sensors; one that’s significantly different is likely bad.
Step 4: Check Sensor Voltage Output
With the sensor plugged in and the car’s ignition on, back-probe the connector with your multimeter set to AC voltage (mV). Slowly rotate the wheel by hand. You should see a small alternating current voltage generated. No voltage or an erratic reading indicates a bad sensor or damaged tone ring.
Step 5: Address Any Found Issues
Based on your inspection and tests:
* Clean a dirty sensor carefully with electrical cleaner.
* Replace a faulty wheel speed sensor. This is a common fix.
* Repair damaged wiring using solder and heat shrink tubing, never just twist and tape.
* Clean corroded connectors with electrical contact cleaner.
* Replace a damaged tone ring. This might require replacing the entire CV axle or hub bearing assembly.
Step 6: Clear Codes and Test Drive
After making repairs, clear all DTCs with your scanner. Take the car for a test drive of at least 10-15 minutes, including some turns and varied speeds. Verify that the check engine light and VSA light remain off and that the system functions normally.
Important Considerations and Cost
Diagnosing this code can sometimes be tricky because it’s a communication code. If you’ve checked all sensors and wiring and the code persists, the issue could be with the VSA module itself. Professional diagnosis with advanced scan tools that can communicate with the ABS/VSA module may be necessary.
Estimated Repair Costs:
* Wheel Speed Sensor (Part Only): $30 – $150 per sensor.
* CV Axle (with tone ring): $150 – $400 per axle.
* Hub Bearing Assembly: $100 – $300 per unit.
* Professional Labor: 1-2 hours of diagnosis and repair, typically $100 – $250 per hour.
Doing the work yourself can save significantly on labor, especially for sensor replacement, which is often straightforward. Always use quality OEM or reputable aftermarket parts for reliable repairs.
FAQ Section
Is it safe to drive with a P1399 code?
You can usually drive the car, but you should do so with caution. Your stability control and traction control will not work. This means in slippery conditions or during emergency maneuvers, the car could skid or lose control more easily. Have the issue diagnosed soon.
Can a bad battery cause a P1399 code?
Yes, a weak or failing battery can cause low system voltage. This low voltage can lead to erratic signals from sensors and modules, potentially triggering codes like P1399. It’s a good idea to have your battery and alternator tested if you see this code alongside other electrical gremlins.
Will P1399 prevent my car from passing inspection?
In most regions, an illuminated check engine light is an automatic failure for emissions or safety inspection. Since P1399 turns on the check engine light, it will likely cause your vehicle to fail until it is repaired.
What’s the difference between P1399 and an ABS code?
P1399 is set by the Engine Control Module (ECM) based on data it receives from the VSA system. A specific ABS or VSA code (usually starting with C) is set by the VSA module itself when it detects a direct fault within its own system. A P1399 often appears alone, while an ABS code can give you the exact wheel location.
Can I reset the P1399 code myself?
Yes, you can clear the code with an OBD-II scanner. However, if the underlying problem is not fixed, the code will come back, usually within one or two drive cycles. Resetting the code is a useful diagnostic step but not a fix.
Dealing with a P1399 code requires patience and a methodical approach. Start with a thorough visual inspection, as many problems are easily visible. Testing the sensors and their wiring is the next logical step. While the system seems complex, fixing it is often within the reach of a careful DIYer with basic tools. If the problem points to the module or after all else fails, consulting a professional technician with Honda-specific diagnostic equipment is the best course of action. Remember, addressing this code restores your vehicle’s important safety features, keeping you secure on the road.