Owner's Problem Description
The owner bought a 1991 Dodge Dynasty and reports that the transmission does not shift out of third gear, leading to redlining at speeds of 55-60 mph. The previous owner mentioned a wire issue related to the transmission. The vehicle currently struggles with proper gear shifting, indicating a potential electrical or mechanical fault.
Professional Technical Analysis
The 1991 Dodge Dynasty equipped with a 3.3L V6 engine and a 4-speed automatic transmission is experiencing a condition commonly referred to as 'limp mode', where the vehicle is limited to lower gears for safety reasons. In this case, it appears the transmission is stuck in third gear, preventing proper shifting and causing the engine to redline at higher speeds. This condition can arise from various issues, including sensor failures, wiring problems, or internal transmission wear. Potential stored diagnostic trouble codes (DTCs) in the Transmission Control Module (TCM) should be retrieved to identify the root cause of the malfunction. The vehicle's transmission system is interconnected; issues in the wiring harness or transmission range sensor can significantly impact shifting behavior. Common fault codes include those related to the transmission fluid temperature sensor, output speed sensor, and range sensor. Given the vehicle's age, it’s essential to consider wear patterns in clutches and seals as well. A thorough inspection of the wiring and connectors entering the transmission is crucial, as intermittent connection issues could lead to erratic shifting behavior. The vehicle's current state poses safety concerns, as operating in limp mode can limit acceleration and create unpredictable driving conditions. Additionally, it’s vital to assess the condition of the transmission fluid for discoloration or burning smells, indicative of potential internal damage. Regularly, Chrysler vehicles from this era show wiring harness degradation and sensor failures, often necessitating replacement of critical components well before 100,000 miles.
Possible Causes
Most common causes (ordered by frequency):
- Transmission Range Sensor Failure: The transmission range sensor, which provides critical input to the TCM regarding gear selection, may be malfunctioning. This could prevent the transmission from shifting properly. Testing the sensor's output voltage and resistance values (typically 5V reference and ground) is essential. If faulty, replacement with OEM part number 4796517AA is recommended. Symptoms often include erratic shifting or failure to shift out of a specific gear. - Stored DTCs related to range sensor failures, erratic shifting behavior, potential voltage readings outside specified range.
- Wiring Harness Issues: The wiring harness connecting the transmission solenoids and sensors may be damaged, resulting in communication failures with the TCM. Inspect the wiring for signs of wear or corrosion, especially near connectors. A common failure pattern includes exposed wires that lead to intermittent faults, which can prevent the transmission from responding to control signals appropriately. - Visual inspection shows frayed wires, possible corrosion at connectors, intermittent shifting issues reported.
- Transmission Fluid Condition: Old or contaminated transmission fluid can lead to shifting issues and reduced hydraulic pressure. Check the fluid level, color (should be red), and smell (should not smell burnt). If the fluid appears dark or has a burnt odor, a fluid change and potential filter replacement may be necessary. OEM transmission fluid part number 68048934AA should be used for replacement. - Fluid inspection reveals dark color or burnt odor, potential fluid contamination affecting shifting performance.
- Internal Transmission Wear: Given the vehicle's age, internal components such as clutch plates and seals may be worn out, leading to inadequate engagement and shifting issues. A comprehensive inspection of the transmission, including checking the clutch volume index (CVI), can provide insights into the condition of the internal components. If wear exceeds acceptable limits, a rebuild may be necessary. - Clutch slippage during manual operation, CVI readings indicating significant wear, possible overheating symptoms.
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 by scanning the vehicle's onboard diagnostics using a professional OBD-II scanner or the GeekOBD APP to retrieve any stored or pending diagnostic trouble codes (DTCs). Pay particular attention to codes associated with the transmission control module, range sensor, and any electrical faults. This initial step will guide further diagnostic efforts and help pinpoint the source of the shifting issue.
- STEP 2 - Visual Inspection of Wiring and Connectors: Conduct a thorough visual inspection of the transmission wiring harness and connectors. Look for any signs of fraying, corrosion, or loose connections. Pay special attention to the transmission range sensor connector, as issues here are common. Repair or replace any damaged wiring or connectors identified during this inspection.
- STEP 3 - Fluid Condition Check: Check the transmission fluid level, color, and odor. If the fluid is low, top it off with the appropriate transmission fluid (OEM part number 68048934AA). If the fluid appears dark or smells burnt, consider performing a fluid change and filter replacement. Document the fluid condition as it can provide insights into potential internal issues.
- STEP 4 - Sensor Testing: Using a multimeter, test the output voltage and resistance of the transmission range sensor. It should provide a steady voltage output when the gear selector is in the correct position. If the readings are outside the specified range, consider replacing the sensor with OEM part number 4796517AA. This step will help verify the functionality of the sensor before considering internal transmission repairs.
