Possible Causes:
* PCM Issues: The PCM is the "brain" of the car. A faulty PCM can cause numerous problems, including triggering both the check engine and airbag lights. A failing PCM might not properly communicate with the various sensors and modules, including the airbag control module. This is a more complex issue requiring professional diagnosis.
* Low Battery Voltage/Electrical Problems: A low battery voltage or other electrical problems can cause erratic sensor readings leading to both lights illuminating. This can include issues with the alternator, battery cables, or even corroded connections.
* Faulty Airbag Control Module (ACM): A malfunctioning airbag control module can directly trigger the airbag light, and depending on how it fails, might also indirectly affect other systems, potentially leading to a check engine light.
* Body Control Module (BCM) Issues: The BCM manages many of the car's electrical systems. A fault here could affect communication between various modules, including the PCM and ACM.
* Loose or Corroded Connections: Check all grounds and connections related to the airbag system and the PCM. Corrosion can interrupt signals and cause malfunctions.
* Shared Wiring Harness Problem: A damaged or compromised wiring harness could affect both systems, causing both lights to illuminate.
Troubleshooting Steps:
1. Check the Battery Voltage: Use a multimeter to check the battery voltage. It should be around 12.6V when the car is off and around 13.5-14.5V when the engine is running. A low voltage can cause intermittent sensor readings.
2. Scan the Codes: You need a code reader (OBD-II scanner) to retrieve diagnostic trouble codes (DTCs) from the PCM. This will give you a starting point for identifying potential issues. Auto parts stores often offer free code scanning services. Note both the check engine and airbag codes, if present.
3. Inspect Wiring: Look for any obvious damage, loose connections, or corrosion in the wiring harnesses related to the airbag system and the PCM. Pay close attention to connectors under the dash, in the engine bay, and near the airbag sensors.
4. Check Fuses and Relays: Check the fuses and relays related to the airbag system and PCM in the fuse box under the hood and inside the car.
What NOT to do:
* Don't attempt to repair the airbag system yourself unless you are a qualified technician. Airbag systems are complex and potentially dangerous. Improper repairs can lead to serious injury or death.
Recommendation:
The most reliable way to diagnose this issue is to take your 1998 Dodge Avenger to a qualified mechanic or auto repair shop. They have the proper tools and expertise to diagnose the problem accurately and safely repair it. Provide them with the diagnostic trouble codes (DTCs) you obtain from a code reader. Given the age of the car, addressing any underlying electrical issues is crucial.
