Owner's Problem Description
The owner reports that their 1996 Dodge Ram B2500 with a 5.2L engine and 120,000 original miles will not start. They have checked all fuses and found them to be okay, but are uncertain about the condition of the relays. The vehicle displays multiple codes indicating high voltage readings from various sensors, suggesting a possible grounding issue. The truck currently does not run, but the owner was able to measure 5 volts on all three throttle position sensor (TPS) leads with the ignition in the 'ON' position.
Professional Technical Analysis
The 1996 Dodge Ram B2500, equipped with a 5.2L V8 engine and approximately 120,000 original miles, is exhibiting a no-start condition. The owner has reported that all fuses are intact, but the status of the relays remains uncertain. Notably, multiple diagnostic trouble codes (DTCs) indicate high voltage readings across several sensors, which suggests a common ground issue impacting the sensor functionality. Given the existence of both signal grounds and power grounds for the Engine Control Module (ECM), it is critical to examine these connections thoroughly. The TPS readings show 5 volts on all three wires, which indicates an open ground in the circuit. This situation can lead to erratic behavior or failure of the ignition system and fuel injectors. The no-start condition necessitates an investigation into the grounding integrity, checking for breaks or corrosion in the ground wires that may lead to high resistance. Current diagnostic codes such as P0123 (TPS high), P0118 (Engine Coolant Temperature Sensor high), and P0113 (Intake Air Temperature Sensor high) further corroborate the potential ground issue affecting multiple systems. Safety precautions should be taken when working near the electrical system, including disconnecting the battery. In summary, a systematic approach is needed to isolate and rectify the grounding problem before further diagnostics on the ignition and fuel systems can be effectively performed.
Possible Causes
Most common causes (ordered by frequency):
- Common Ground Wire Failure: The presence of high voltage codes across multiple sensors suggests a break in the ground wire common to these components. Given that there are multiple ground connections for the ECM, including signal grounds for sensors and power grounds for high-current devices, it is critical to inspect these connections. If the signal grounds are compromised, it can lead to erroneous voltage readings on the TPS and other sensors. - Diagnostic trouble codes P0123, P0118, and P0113 indicate high voltage readings; all TPS wires show 5 volts.
- Throttle Position Sensor (TPS) Failure: Although the TPS is showing 5 volts across all leads, it may still be faulty if the internal resistances are out of specification. The expected voltages on the TPS wires should range from 0.2 volts (closed throttle) to around 4.5 volts (wide open throttle). An internal failure can cause it to read high across all leads. - TPS readings remain at 5 volts even with the throttle closed, indicating possible internal failure.
- Ignition Relay Malfunction: Given the uncertainty regarding the relays, a faulty ignition relay could prevent power from reaching the ignition system. Testing the relay for continuity and performance under load is essential to ensure it operates correctly. - No ignition or fuel pump operation suggests a possible relay issue; testing required to confirm functionality.
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 - Initial OBD-II Diagnosis: Begin with a thorough scan using an OBD-II scanner or GeekOBD APP to retrieve trouble codes and analyze live data. Pay particular attention to any high voltage codes and freeze frame data to understand the conditions under which they were set. This will help identify if there's a common ground issue affecting multiple sensors.
- STEP 2 - Ground Wire Inspection: Visually inspect and test all ground connections related to the ECM and sensors. Use a multimeter to measure resistance between the ground connections and battery negative terminal; values should be less than 5 ohms. Look for signs of corrosion or damage that could cause high resistance.
- STEP 3 - Relay Testing: Check the ignition relay for continuity and proper operation. With the relay removed, perform a continuity test using a multimeter; it should show continuity in the closed position. Then, test the relay under load conditions to ensure it activates the ignition system appropriately.
- STEP 4 - TPS Voltage Verification: With the ignition on, measure the voltage at each TPS lead. The readings should be approximately 0.2 volts (closed throttle), 0.5 volts (idle), and up to 4.5 volts (wide open throttle). If all leads read 5 volts, further investigation into the TPS or wiring is necessary.
