* P1131: Heated Oxygen Sensor (HO2S) Heater Circuit Malfunction (Bank 1, Sensor 1) – This means the heater element within the oxygen sensor isn't working correctly. The heater is crucial for the sensor to function properly, especially during cold starts.
* P1137: Oxygen Sensor Circuit Low Voltage (Bank 1, Sensor 1) – This indicates a problem with the sensor's signal voltage. This could be due to a faulty sensor, wiring issues, or other problems affecting the sensor's readings.
Since you've already addressed some basic maintenance (air filter, fuel system flush, spark plugs), the problem likely lies within the oxygen sensor circuit itself. Here's a systematic approach to troubleshooting:
1. Verify the Codes: Double-check that the codes are still present after clearing them with a scan tool. Some cheap OBD-II readers might not accurately read these codes, so a higher-quality one is recommended.
2. Inspect the Wiring and Connector (Bank 1, Sensor 1):
* Location: Find the upstream oxygen sensor (Sensor 1) on bank 1. This is the sensor located closest to the engine's exhaust manifold. Consult a repair manual or online diagram for the exact location on your 1999 Contour.
* Visual Inspection: Carefully examine the wiring harness leading to the oxygen sensor. Look for any:
* Broken wires: These are often caused by chafing against the engine or exhaust components.
* Corrosion: Check the connector for corrosion or damage to the pins. Clean it with electrical contact cleaner if necessary.
* Loose Connections: Make sure the connector is securely plugged into the sensor and the wiring harness.
3. Check the Oxygen Sensor (Bank 1, Sensor 1):
* Resistance Test (Optional, requires a multimeter): A multimeter can test the sensor's resistance. You'll need a repair manual to find the correct resistance specifications for your sensor. A significantly deviating resistance value suggests a faulty sensor. This test is more complex and requires knowledge of electrical testing.
* Replacement: If the wiring looks good, the most likely culprit is a faulty oxygen sensor itself. Replacing the upstream oxygen sensor (Bank 1, Sensor 1) is often the solution for these codes. Ensure you get a sensor specifically designed for your 1999 Ford Contour.
4. Other Potential Issues (Less Likely but Possible):
* Exhaust Leaks: A significant exhaust leak before the sensor can affect readings. Inspect the exhaust system for leaks.
* Catalyst Converter Issues: A failing catalytic converter can also impact oxygen sensor readings. This is less likely to cause *just* P1131 and P1137, but it's worth considering if other symptoms are present (reduced power, unusual exhaust smell).
* PCM (Powertrain Control Module) Problem: While less common, a faulty PCM could also contribute. This is usually diagnosed through more advanced diagnostics.
Important Notes:
* Repair Manual: A repair manual specific to your 1999 Ford Contour is highly recommended. It will provide detailed diagrams, specifications, and troubleshooting steps.
* Safety: Exhaust systems get extremely hot. Allow the system to cool down completely before working on it.
* Professional Help: If you're not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic.
Start with the visual inspection and connector checks. If those are clean, replacing the oxygen sensor is the next most logical step. Remember to clear the codes after making any repairs to see if the problem is resolved.
