Why Your 2014 Honda Accord FDW/LDW Lights Are On (And It’s NOT the Camera)
Introduction
You bring your car in with the forward collision warning (FCW) and lane departure warning (LDW) lights lit up on the dash. First thought? Most people assume the camera is bad. Maybe the windshield needs calibration. Maybe it’s an expensive ADAS issue.
That’s exactly how people get burned.
In this case, the real problem had nothing to do with the camera system at all. It was a transmission-related fault that shut the entire safety system down. If you don’t understand how these systems communicate, you’ll end up replacing the wrong parts and wasting time and money.
Let’s walk through this step by step like we would in the shop.
🔧 Recommended Tools for Diagnostics
When you're diagnosing modern vehicles, having the right tools makes all the difference. A basic code reader will only get you so far—you need tools that let you see what’s really going on and test components properly.
Autel MaxiSys MS906 Pro TS Professional OBD2 Scanner (with TPMS & full system diagnostics)
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This tool gives you full system access, not just engine codes. You can pull data from transmission, ABS, and driver assist systems, which is critical for proper automotive troubleshooting.
Power Probe 3 (PP3CSRED) Circuit Testing Tool
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This is something I use daily. It allows you to quickly check power, ground, and even activate components to verify operation without guessing.
Power Probe ECT3000 Circuit Tracer (Short & Open Finder)
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When you're chasing wiring issues, this tool saves hours. It helps locate opens and shorts without tearing the vehicle apart.
Vehicle Overview
This case involves a 2014 Honda Accord 4-cylinder, a very common vehicle known for reliability—but like all modern cars, it relies heavily on communication between modules.
Mileage wasn’t the issue here. The problem was electronic, not wear-and-tear related.
Vehicle Concern
The main symptoms were:
Forward Collision Warning (FCW) light ON
Lane Departure Warning (LDW) light ON
No obvious drivability complaints were reported, which made this a classic case of warning lights without clear symptoms—something you see a lot when diagnosing car problems on newer vehicles.
Initial Inspection & Observations
At first glance, nothing stood out physically. No damage to the windshield, no visible obstruction to the camera, and no signs of recent body work.
That’s important.
Because when both FDW and LDW lights come on together, most people immediately suspect the camera system. But experience tells you to check the network first, not just the component.
Diagnostic Trouble Codes
A full system scan revealed:
P0843 – Transmission Fluid Pressure Switch “A” Circuit High
U0402 – Invalid Data Received from PCM/TCM
U0416 – Invalid Data Received from VSA Module
Here’s where many techs go wrong.
They see the ADAS warning lights and start chasing camera issues, ignoring the transmission code. That’s a mistake.
Step-by-Step Diagnostic Process
When diagnosing car problems like this, you have to think in terms of system communication, not just individual parts.
First, I focused on the P0843 code. This code indicates that the transmission control module is seeing a pressure signal that’s stuck high. That means either the switch is faulty, or the circuit has an electrical issue.
Now here’s the key: the powertrain control module (PCM) shares data with multiple systems, including the stability control (VSA) and the forward collision/lane departure system.
If the PCM is reporting unreliable data, other modules stop trusting it.
That’s exactly what happened here.
The VSA module picked up on the bad data and flagged it. Then the FCW/LDW system, which depends on accurate vehicle speed, braking, and torque data, shut itself down as a safety measure.
That’s why those lights were on.
Not because the camera was bad—but because the system couldn’t trust the information it was receiving.
Next step was to physically verify the suspected failure.
The transmission fluid pressure switch “A” on this Accord is mounted externally on the transmission, but it’s not immediately visible. It’s located on the upper front side of the transmission, underneath the air intake box.
This is where things got interesting.
The vehicle had already been diagnosed previously. The correct part had been recommended—but it was never installed. One technician ordered the wrong part, and another assumed the component was internal and didn’t proceed.
This is a perfect example of how poor follow-through can lead to repeated misdiagnosis.
Once the air box was removed, the pressure switch location was confirmed. It’s a small, threaded, two-wire sensor mounted directly into the transmission case.
Exactly where it should be.
Key Findings
The root cause of the issue was:
A faulty transmission fluid pressure switch “A”
The part had never been replaced despite prior diagnosis
Everything else—the warning lights, the communication codes—were simply symptoms of that failure.
Final Diagnosis & Repair Recommendation
Replace the transmission fluid pressure switch “A,” clear all codes, and perform a road test.
Once the faulty signal is corrected, the PCM will begin sending valid data again. That allows the VSA and FCW/LDW systems to come back online.
No camera replacement. No calibration. No unnecessary parts.
Just proper automotive troubleshooting.
Common Causes of This Problem
This issue isn’t unique. Common causes include:
Failed transmission pressure switch
Wiring issues (short to voltage)
Connector contamination (fluid intrusion)
Misdiagnosis due to unrelated warning lights
This is why understanding how systems interact is critical when diagnosing car problems.
Lessons for DIYers & Used Car Buyers
This is a textbook example of how modern vehicles can mislead you.
Warning lights don’t always point directly to the faulty component. In many cases, they’re just reacting to bad data from somewhere else.
If you’re doing your own automotive troubleshooting, don’t jump straight to replacing parts based on symptoms alone.
And if you’re buying a used car, pay close attention to warning lights like FCW or LDW. They may seem minor, but they can be tied to deeper issues that weren’t properly diagnosed.
This is also a great example of why incomplete repairs—like ordering the wrong part or failing to follow through—can drag out a simple fix for months.
Don’t Get Burned on Your Next Used Car
If you’re thinking about buying a used car—or even if you already have one—this is exactly the kind of problem that can slip through the cracks and cost you big money later.
After 35+ years in the automotive field, I’ve seen firsthand how often people end up with vehicles that have hidden issues just like this.
That’s why I put together a simple Used Car Guide to help you understand what to look for and how to avoid making a costly mistake.
It’s a quick, practical guide designed to give you the right mindset and approach before you buy.
👉 Get the guide here:
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It’s a smart first step toward making a better used car decision.
Disclaimer: Some of the links in this post may be affiliate links, which means I may earn a small commission if you purchase through them—at no additional cost to you. I only recommend tools and products that I personally use or trust in real-world diagnostics.
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