Owner's Problem Description
The owner reports that their 1999 Cadillac DeVille stalls at stop signs when it rains heavily, particularly when in gear and the brake is applied. The issue resolves once the engine warms up. This problem is consistent only during wet conditions and has not occurred during dry weather. The owner recalls a similar issue in a previous vehicle due to a cracked distributor cap but notes that the current cap appears different and long. They are concerned about the repair costs associated with Cadillacs.
Professional Technical Analysis
The 1999 Cadillac DeVille, equipped with a 4.6L V8 engine and an automatic transmission, has a reported issue of stalling during heavy rain conditions, particularly at stops with the brake applied. The vehicle has an estimated mileage of around 120,000 miles. The owner notes that the stalling occurs until the engine reaches normal operating temperature, suggesting potential electrical or sensor issues exacerbated by moisture. This symptom pattern indicates a possible failure in components prone to water intrusion, such as the ignition system or engine management sensors. Given the age of the vehicle, common issues include degradation of connectors and insulation on wires, particularly in humid environments. The stalling could be linked to a faulty ignition control module (ICM) or issues with the crankshaft position sensor (CPS), both of which are sensitive to moisture. Furthermore, if the vehicle has been exposed to high humidity or water, it could lead to corrosion or shorts in the electrical systems, impacting performance. The owner’s previous experience with a cracked distributor cap highlights a common failure point in older vehicles, though modern engines typically utilize coil-on-plug designs. A thorough inspection of the ignition system, including checking for moisture in the spark plug wells and ensuring all connections are secure and free of corrosion, is warranted. Potential fault codes related to the ignition or engine performance should also be retrieved and analyzed using an OBD-II scanner to guide diagnosis.
Possible Causes
Most common causes (ordered by frequency):
- Moisture Ingress in Ignition System: Water intrusion into the ignition system can lead to misfire or stalling. The ignition coils, especially if they are older, may not be sealed properly and can allow moisture to affect their operation. Testing the coils for resistance (typically 0.5-1.5 ohms) and inspecting for any visible signs of degradation or corrosion will be essential. This is especially common in humid environments and can lead to erratic spark output. - Engine misfires during rain, visual inspection reveals potential water accumulation around ignition components, resistance testing shows inconsistencies.
- Faulty Crankshaft Position Sensor (CPS): The CPS can become affected by moisture, leading to incorrect readings and stalling. This sensor is crucial for engine timing and may show erratic signals when wet. Testing the CPS should involve checking the voltage output (typically around 0.5-4.5V) while monitoring for consistent readings. A faulty CPS can lead to stalling conditions, especially in adverse weather. - CPS readings fluctuate during rain, potential stored fault codes in PCM related to crankshaft position, stalling observed during live data monitoring.
- Electrical Connector Corrosion: Corrosion at electrical connectors can impair signal integrity, especially under humid conditions. It’s critical to inspect and clean connectors, particularly those related to the ignition system and PCM. A multimeter can be used to check for continuity and resistance (should be less than 5 ohms). If corrosion is present, connectors should be replaced or repaired as necessary. - Visual inspection shows corrosion on connectors, continuity tests fail on affected connections, intermittent stalling correlates with moisture exposure.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - OBD-II Scan: Begin with a comprehensive scan of the vehicle's onboard diagnostics using a professional OBD-II scanner or the GeekOBD APP to retrieve any stored trouble codes. Look for codes related to the ignition system, engine performance, or the crankshaft position sensor. This will provide insight into any underlying issues that may be contributing to the stalling condition.
- STEP 2 - Visual Inspection: Conduct a thorough visual inspection of the ignition system components, including the ignition coils, spark plugs, and any exposed electrical connectors. Check for signs of moisture, corrosion, or physical damage. Ensure that all connections are tight and free from debris. This step is crucial for identifying issues that may not trigger fault codes but can still cause stalling.
- STEP 3 - Component Testing: Test ignition coils for resistance values using a digital multimeter, ensuring they fall within the specified range of 0.5-1.5 ohms. Additionally, check the crankshaft position sensor output voltage while cranking the engine to confirm it produces consistent readings (should range from 0.5 to 4.5V). Document any anomalies observed during testing.
- STEP 4 - Road Test: Conduct a controlled road test under similar conditions to when the stalling occurs, preferably during rain if possible. Monitor live data with the GeekOBD APP, focusing on the ignition system parameters and crankshaft position sensor readings. Look for any discrepancies that occur during the symptoms to help isolate the problematic component.
