2002 Mitsubishi Colt CJ 1.6 Manual Limp Mode, Check Engine Light & Rev Counter Issue
I have a 2002 Mitsubishi Colt CJ 1.6 manual. The check engine light is on, the rev counter doesn’t work, and it feels like it’s in limp mode with low power. If I disconnect and reconnect the battery it drives нормально for about 5–10 miles, then the problem returns. A Launch scanner only shows P0300 (random misfire). I’ve replaced the spark plugs, coil packs, leads, crank sensor, and did an oil and filter change.
You’ve got a classic electrical dropout. The fact that the tachometer dies, you lose power, and a battery reset temporarily clears it points to a loss of crank/cam signal to the ECM or the ECM itself glitching. Since you’ve already replaced the crank sensor, plugs, coils, and leads, and you get a P0300 with limp mode, the next most likely culprit is a failing ECM or a wiring/ground issue at the ECM or main engine harness connector. The battery reset temporarily clears the fault, which is typical of an ECM or power/ground supply issue, not a mechanical or basic ignition problem.
If the ECM loses crank signal, you’d get no tach and limp mode. But you’ve replaced the sensor, so unless the wiring is bad, the ECM itself is suspect.
Most likely culprits
- Failing Engine Control Module (ECM) — Fits the intermittent, resettable electrical dropout and limp mode.
- Wiring/ground issue at ECM or main harness — Could cause loss of crank signal and ECM reset, especially if movement or heat triggers it.
- Power supply relay or fuse issue — Less likely, but if ECM power drops out, you’d see similar symptoms.
How to narrow it down
- Wiggle test the main engine harness and ECM connectors with the engine running. If the tach or engine stumbles, you’ve found a wiring/connector issue.
- Check ECM grounds and power feeds (especially at the battery, chassis, and ECM case). Clean and retighten all ground points.
- Monitor live data for crank/cam signal dropout while the problem is happening. If both signals drop out, suspect ECM or power supply.
- Check for water ingress or corrosion at the ECM and harness connectors.
- Swap in a known-good ECM (if available) as a last step. If the problem disappears, your ECM is toast.
Possible parts (if needed)
- Engine Control Module (ECM)
- Main engine harness connector (clean/repair, not usually replaced)
A few questions
- When the tach dies, do any other dash lights flicker or does the speedo drop out?
- Has the car had any water leaks, battery swaps, or jump-starts recently?
- Does the problem happen more when hot, cold, or after hitting bumps?
If you get a tach drop and limp mode together, and a battery reset fixes it for a bit, you’re almost certainly looking at an ECM or its power/ground supply. If you’re not comfortable checking harnesses and ECM pins, this is about the point I’d call in a pro with a scope and wiring diagrams.