Ways water intrusion can trigger the service engine light:
* Sensors: Many critical engine sensors (like the mass airflow sensor (MAF), crankshaft position sensor (CKP), camshaft position sensor (CMP), oxygen sensors (O2), etc.) are sensitive to moisture. Water can short-circuit these sensors, leading to inaccurate readings. The car's computer recognizes these faulty readings as a problem and illuminates the check engine light (or service engine soon light).
* Wiring and connectors: Water can corrode wiring harnesses and connectors, creating open circuits or short circuits. This can disrupt the communication between various engine components and the computer, triggering the light.
* Engine control module (ECM) / Powertrain Control Module (PCM): Although relatively well-protected, significant water intrusion (like a flood) can damage the ECM/PCM itself. This is the car's "brain" and a failure here will almost certainly cause a service engine light and many other problems.
* Ignition system: Water can cause short circuits in the ignition system components, impacting the ignition timing or spark delivery. This can lead to misfires and set off a check engine light.
Damage from water intrusion:
The damage can range from minor to catastrophic:
* Minor: Corrosion on connectors, requiring cleaning and possibly replacement of connectors.
* Moderate: Sensor failure, requiring sensor replacement.
* Severe: Damaged wiring harnesses needing extensive repair or replacement. A damaged ECM/PCM might require a very expensive replacement. Significant engine damage is possible from prolonged misfires or other malfunctions caused by water intrusion.
What to do if your service engine light comes on and you suspect water:
1. Identify the source of water: Where did the water get in? This is crucial in preventing future problems. Common culprits are leaks in the windshield, sunroof, or seals around doors and windows.
2. Don't drive if there's standing water: If you've driven through significant water or suspect major water intrusion, avoid driving until it's checked. Driving with severely compromised electrical systems could cause further damage.
3. Have it professionally diagnosed: Take your car to a mechanic. They can use a diagnostic scan tool to read the trouble codes stored by the car's computer. This will pinpoint the exact problem.
4. Address the water leak: After the engine light issue is fixed, be sure to address the root cause of the water intrusion. Ignoring this will likely lead to recurring problems.
In short, while water doesn't directly *cause* the light, it creates conditions that can lead to malfunctions causing the light to come on. Professional diagnosis and repair are always recommended in this situation.
