Why won't the check engine light on my Mitsubishi Expo go off?

Short answer: A check-engine light on an Expo with code P0340 means the computer isn't getting a good camshaft position signal. Check the sensor, its wiring and plug, and make sure the timing belt marks line up, especially after a belt job. A knock going uphill when warm points to the EGR system. Check its valve and vacuum lines.

Symptom: The check-engine light stays on, or the engine knocks or pings under load once warmed up.

What to check first

1. Get the exact code number read.
2. Check the cam sensor connector and wiring for damage.
3. Confirm the timing belt marks line up.
4. For knock, check that the EGR valve opens and its vacuum lines are intact.
5. Use the gas grade the owner's manual calls for.

Likely causes

1. Camshaft position sensor or its wiring. This sensor tells the computer where the camshaft is. A bad sensor, connector or wire sets the code.
2. Timing belt off a tooth. If the timing belt was replaced and isn't lined up exactly, the cam and crank signals disagree.
3. Engine computer fault. Less often, the computer itself is the problem after everything else checks out.
4. EGR system not working. The exhaust gas recirculation (EGR) valve sends a little exhaust back in to cool combustion. If it or its vacuum lines fail, the engine can knock under load.

What it usually costs

Owners didn't post prices.

Is it safe to keep driving?

A cam sensor code may cause stalling. Heavy knocking under load can damage the engine, so ease off and get it checked.

DIY or shop?

Checking vacuum lines and connectors is DIY. Timing and sensor diagnosis is usually a shop job.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists 2 recall(s) for the Mitsubishi Expo in these years, and none match this problem. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 2 keyword-matched complaints for Mitsubishi Expo 1992–1995 (of 90 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-29; keywords: check engine, engine light, knock, stall, idle, egr) (NHTSA returned no data for 4 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 95 Mitsubishi Expo - mechanic unable to fix check engine light on Car Talk, a 1995 Expo had a check-engine light on for years and couldn't pass a California smog check. The code was P0340 (camshaft position sensor circuit). Members asked whether the timing belt had been replaced and the marks lined up. The owner's mechanic tried timing adjustments without success and planned a used computer next.
• In Engine Knock - 92 Mistubishi Expo SP - 196k on Car Talk, a 1992 Expo SP with the 2.4 liter and 196,000 miles started knocking when warm going up steep highway grades. Fuel and a tune-up didn't help. A member said to check the EGR valve, its diaphragm and its vacuum lines.

Quick tip

If the code came on after a timing belt job, have the belt timing rechecked before buying parts.

Vehicle focus: Mitsubishi Expo and Expo LRV, 1992-1995.

Safety / mechanic note

Stalling and engine knock are safety items. Verify with a mechanic.