Owner's Problem Description
The owner reports that their 1991 Pontiac Sunbird will not start, even though there is power to the solenoid. When the key is turned to the crank position, the engine does not crank. Previously, the starter solenoid was replaced, and the vehicle was functioning well until this issue arose. The current condition indicates a persistent no-start problem that requires further investigation.
Professional Technical Analysis
This 1991 Pontiac Sunbird, equipped with a 2.0L 4-cylinder engine and an automatic transmission, is experiencing a no-start condition, reported by the owner as occurring when attempting to crank the engine. The vehicle has a history of a replaced starter solenoid which initially resolved starting issues. The current failure to start suggests potential electrical system malfunctions, specifically concerning the ignition system or neutral safety switch. When the key is turned to the crank position, the ignition feed should energize the starter solenoid via the purple wire, which is routed through the neutral switch—this route must be verified. A key aspect of diagnosis is to ensure that battery voltage (approximately 12.6V) is present at the starter solenoid at all times, and that the ignition feed wire supplies voltage when the key is in the crank position. Testing should also confirm that the transmission is in park or neutral and that the parking brake is applied. Symptoms may also indicate a faulty ignition switch or neutral safety switch, which are common failure points in this model. Given the vehicle's age and typical mileage of around 100,000 miles, wear in these components could lead to intermittent failures. The current condition lacks any warning lights, which further indicates a potential electrical issue rather than a mechanical failure, necessitating thorough testing of the electrical circuits involved in the starting system.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Ignition Switch: The ignition switch may not be providing power to the starter solenoid when the key is turned to the crank position. This is common in older vehicles like the 1991 Sunbird, where wear can cause internal contacts to fail. Testing the ignition switch with a multimeter can confirm if it is outputting the necessary voltage (around 12V) when cranking. - No voltage at the ignition feed wire when the key is turned to crank, multimeter readings showing open circuit.
- Neutral Safety Switch Malfunction: The neutral safety switch prevents the vehicle from starting unless in park or neutral. If this switch is faulty, it may not allow the starter to engage even with power present. Testing the switch by bypassing it temporarily can help determine if it is the source of the issue. - Starter engages when bypassing the neutral safety switch, indicating the switch is defective.
- Starter Motor Failure: The starter motor itself could be faulty. Symptoms may include a clicking sound but no engagement. Testing the starter motor directly by applying battery voltage can confirm if it is functional. Common issues include worn brushes or internal shorts. - Clicking sound from the starter, no cranking, voltage applied directly results in no activity from the starter motor.
- Wiring Issues: Corrosion or damage to wiring between the ignition switch, neutral safety switch, and starter solenoid can create poor connections, leading to failure in starting. Inspecting wiring for frays, corrosion, or loose connections is essential. - Visual inspection reveals frayed wires or corroded connectors, resistance measured across connections shows high values.
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 Voltage Check: Begin by using a multimeter to check for battery voltage at the starter solenoid. Ensure there is a constant 12.6V at the battery terminal and that the ignition feed wire shows voltage when the key is turned to the crank position. This step confirms whether power is reaching the solenoid as expected.
- STEP 2 - Ignition Switch Testing: Test the ignition switch by removing it and checking continuity across the contacts with the key in the crank position. Confirm that voltage is being supplied to the ignition feed wire. If continuity is absent, the ignition switch is likely faulty and requires replacement.
- STEP 3 - Neutral Safety Switch Evaluation: To test the neutral safety switch, locate it and use a multimeter to check for continuity in both park and neutral positions. If it fails continuity tests, it may need replacement. Bypassing the switch temporarily can help identify if it is the cause of the no-start condition.
- STEP 4 - Starter Motor Function Test: If the ignition and neutral safety switches are functioning, test the starter motor by applying battery voltage directly. If the starter engages properly, attention should shift to wiring and connections. If it does not engage, replace the starter.
