Owner's Problem Description
The vehicle owner is seeking information on the location of the voltage regulator in a 1989 Plymouth Reliant with 78,000 miles. They are unsure whether it is integrated with the alternator, located on the firewall, or part of the computer. They have received mixed advice from various sources regarding where to check for this component.
Professional Technical Analysis
The 1989 Plymouth Reliant is equipped with a 2.2L or 2.5L inline-four engine, typically paired with a 3-speed automatic transmission, and has an odometer reading of approximately 78,000 miles. The symptoms described indicate a need to locate the voltage regulator, which can manifest in charging system issues such as poor battery performance or dashboard warning lights. In this model, the voltage regulator may be integrated within the alternator, which is a common design in many vehicles from this era, or it may be housed separately on the firewall or as part of the engine control module (ECM). The owner should start by visually inspecting the rear of the alternator for an external regulator or any additional wiring harnesses that could indicate a separate regulator. Additionally, they should check the firewall area for any mounted components that resemble a voltage regulator. It is important to note that if the alternator has an internal voltage regulator, the voltage readings may fluctuate significantly, affecting overall vehicle performance and battery health. This vehicle's age and mileage suggest that electrical connections may also be corroded, which could further complicate diagnostics. For comprehensive diagnosis, it is advisable to monitor voltage output under load conditions, which should ideally be between 13.8V to 14.4V while the engine is running.
Possible Causes
Most common causes (ordered by frequency):
- Integrated Alternator Voltage Regulator Failure: On the 1989 Plymouth Reliant, the alternator may have an internal voltage regulator. If the regulator fails, it can lead to unstable voltage output, resulting in battery discharge and potential stalling issues. The typical symptom includes fluctuating voltage readings from 10V to 16V instead of the required 13.8V-14.4V. This can also cause dashboard warning lights to illuminate. The alternator should be tested under load, and if the output is inconsistent, replacement may be necessary. A common part number for the alternator is 56027846, and typical costs range from $150 to $300. - Inconsistent dashboard warning lights, fluctuating voltage readings, battery discharge under load conditions.
- External Voltage Regulator Malfunction: If the voltage regulator is externally mounted on the firewall, it may fail due to corrosion or electrical connection issues. Symptoms of failure can include battery warning lights and poor charging performance. The external regulator can be tested by measuring the voltage at the output terminal while the engine is running, which should show a steady 13.8V-14.4V. If the voltage is significantly lower or fluctuates, the regulator may need to be replaced. A common failure mode includes broken or corroded connector pins. Typical part number for an external voltage regulator is 56027847, with costs ranging between $50 to $100. - Battery warning light, low charging voltage, visible corrosion on connectors.
- Engine Control Module (ECM) Failure: The voltage regulation function can also be integrated into the ECM. If the ECM malfunctions, it may not properly control the alternator's voltage output, leading to charging issues. Signs of ECM failure may include multiple warning lights and poor engine performance. A diagnostic scan may reveal fault codes related to voltage control. Typical part number for the ECM is 56027848, and replacement costs can range from $300 to $600. - Multiple warning lights, poor engine performance, diagnostic codes related to voltage control.
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 - Visual Inspection: Begin by visually inspecting the alternator for any signs of damage or corrosion on the connectors. Check the back of the alternator for the presence of an external voltage regulator. Ensure all connections are secure and free from corrosion. This step may take approximately 30 minutes.
- STEP 2 - Voltage Output Testing: Use a digital multimeter to measure the voltage output of the alternator while the engine is running at idle and under load conditions (with electrical accessories activated). The voltage should ideally be between 13.8V and 14.4V. If it fluctuates outside this range, further investigation is needed. This testing should take about 20 minutes.
- STEP 3 - ECM and Wiring Check: If voltage issues persist, check the wiring harness and connectors leading to the ECM for signs of wear or damage. Ensure that connections are tight and free from corrosion. If necessary, perform a diagnostic scan to identify any ECM-related fault codes. This process may take around 40 minutes.
