1991-92 Eclipse, Talon & Laser ECM: Diagnosing and Solving Capacitor Failure

The Inevitable Failure: Leaking Capacitors

The single most common and well-documented problem with the original ECM in the 1991-1992 Eclipse, Talon, and Laser is the failure of its internal electrolytic capacitors. Due to age and countless heat cycles inside the dashboard, these components leak an acidic fluid called electrolyte. This fluid is highly corrosive and eats away at the copper traces and components on the ECM's printed circuit board, leading to short circuits and a wide range of bizarre, intermittent problems. If your vehicle still has its original ECM, it is not a matter of if it will fail from leaking capacitors, but when.

Symptoms of a Failing ECM

A failing ECM due to capacitor leakage can cause a frustrating variety of symptoms that may come and go. Because the ECM controls nearly every aspect of the engine, the signs of failure can be misleading and often mimic other problems.

Starting and Stalling Issues

• No-Start or Hard Starting: The engine cranks but refuses to start, or only starts after many attempts.
• Random Stalling: The engine shuts off unexpectedly while driving, sometimes with the Check Engine Light coming on right as it dies.
• Engine Won't Start, But Boost Gauge is at Zero: On turbo models, if the boost gauge doesn't move at all when you turn the key on, it's a strong sign the ECM is not powering up.

Unusual Sounds and Smells

• Rapid Clicking/Chattering: A fast clicking sound from under the dash is often the fuel pump relay being rapidly cycled on and off by a malfunctioning ECM.
• Fishy or Rotten Seafood Smell: This distinct and unpleasant odor coming from the center console area is the smell of the leaking electrolyte from the capacitors.

Poor Drivability

• Erratic or surging idle.
• Engine hesitation, misfires, or stuttering under acceleration.
• Sudden loss of power that may correct itself.
• Poor fuel economy.

How to Diagnose a Bad ECM

Diagnosing a bad ECM on these cars involves two main steps: a physical inspection and checking for trouble codes.

Step 1: Physical Inspection (The Most Important Step)

The most definitive way to confirm a bad ECM is to remove it and inspect the internal circuit board. The ECM is located in the center console, behind the radio and climate controls.

1. Disconnect the negative battery terminal.
2. Remove the carpeted kick panels on both the driver and passenger sides of the center console. They are typically held by a few screws.
3. You will see the metal case of the ECM. It is held in by three or four 10mm bolts.
4. Unplug the three large yellow wiring harness connectors from the ECM and remove it from the vehicle.
5. Once removed, open the metal case by removing the screws on the top and bottom covers.
6. Carefully inspect the circuit board, paying close attention to the area around the three large cylindrical capacitors. Look for a dark, crusty residue on the board, green or black corrosion on component legs, or any areas that look burnt or discolored. A fishy smell is also a dead giveaway.

Step 2: Reading OBD-I Trouble Codes

These vehicles use a pre-OBD-II diagnostic system. You can retrieve codes without a scanner using an analog voltmeter or a simple 12V LED.

1. Locate the 12-pin diagnostic connector. It's usually attached to the fuse box under the driver's side dashboard, near your left foot.
2. Connect the positive lead of your voltmeter or LED to pin #1 (top right) and the negative lead to pin #12 (bottom left, a ground).
3. Turn the ignition key to the 'ON' position (do not start the engine).
4. The voltmeter needle will sweep or the LED will flash to indicate codes. Long sweeps/flashes represent the 'tens' digit, and short sweeps/flashes represent the 'ones' digit. For example, four long flashes followed by three short flashes is Code 43.

Common codes related to capacitor failure include:

• Code 11: Engine Control Unit (ECU) Failure.
• Code 43: EGR (California models) - This code often appears falsely when the ECM is failing due to capacitor leakage.
• Code 44: Ignition Coil - Like Code 43, this can also be a phantom code caused by a faulty ECM.

Buying a Used Engine Control Module (ECM)

Since new OEM units are no longer available, your options are a used OEM, a remanufactured unit, or a repair service. Here’s what you need to know when buying.

Compatibility is Crucial

This specific ECM, part number MD165530 (or Mitsubishi Electric part number E2T36574), fits a very narrow range of vehicles: 1991-1992 Mitsubishi Eclipse, 1991 Eagle Talon, and 1991 Plymouth Laser models equipped with the 2.0L Turbo engine, a Front-Wheel Drive (FWD) Automatic Transmission, and California Emissions. You must match the part number exactly. An ECM from an AWD, manual transmission, or federal emissions car will not work correctly.

NO Programming Required

This is the most important takeaway for buyers. ECMs for these 1991-1992 vehicles are plug-and-play. They do not need to be programmed, flashed, or matched to your vehicle's VIN. There is no immobilizer or anti-theft system to worry about. If a seller of a 'remanufactured' unit asks for your VIN, it is likely only to confirm they are sending you the correct part number for your application.

What to Inspect on a Used ECM

• Demand Internal Photos: Never buy a used or 'remanufactured' ECM for these cars without seeing clear, high-quality pictures of the internal circuit board. If a seller won't open the case, walk away.
• Look for Cleanliness: The board should be clean, with no dark, sticky residue or green/white corrosion, especially around the capacitors.
• Check the Capacitors: A properly 'remanufactured' unit will have three new capacitors. Check the solder work to ensure it is clean and professional.
• Avoid Damaged Boards: Look for burnt spots, lifted copper traces, or messy-looking previous repair attempts (sometimes called 'spaghetti wires'). A board with significant corrosion damage may not be reliable even after being repaired.

Cost Comparison

Frequently Asked Questions (FAQ)