Pick-ups and Monteros with gasoline engines from 1985 incorporate a dashboard light to remind the owner of necessary maintenance intervals. Reading either "Check EGR" (1985-87) or "Maintenance Reqd" (1988-95), these lights are controlled by the elapsed mileage on the odometer. The light will illuminate first at 50,000 miles (80,000 km) and then at 100,000 miles (160,000 km). 1989 and later vehicles will energize the light at 80,000 (128,000 km) and 120,000 miles (192,000 km) as well. The light is simply a reminder that system maintenance and inspection is due at these intervals; it is not a warning light in the usual sense.
See Figure 1
When the light comes on, resist the temptation to simply turn it off. Leave it on until you have the time to perform at least basic maintenance. Chances are that your Pick-up or Montero is running pretty well at 50,000 miles. A good tune up with fresh filters will keep it that way. Check the vacuum hoses for cracks or damage. Check the EGR valve using the procedure outlined in this section. If this maintenance isn't possible, at least take the vehicle to a dealer or service station capable of running it on an exhaust analyzer. The content of the exhaust gas can tell you quite a bit about how efficiently the engine is burning fuel.
Once the needed maintenance has been performed, the reminder light may be turned off (which resets it for the next interval) by moving a small switch. On 1985-86 Pick-ups, the switch is located on the back of the instrument cluster at the top. Reaching it behind the dashboard can require contortions and creative language, but it can be done without removing the instrument cluster. On 1987-95 Pick-ups and 1990-95 Monteros, the switch is on the front of the instrument cluster, at the bottom right; the clear plastic window over the cluster must be removed to gain access. Carefully remove the four screws and the lens, reset the switch and reinstall the lens.
All 1985-89 Monteros have the reset switch located on the back of the speedometer, roughly behind the 80 mph (128 km/h) marking. Again, reaching it can be difficult, but it can be done. When reaching up behind the dashboard, be careful not to dislodge any wiring harnesses or connectors; don't force or push any components out of the way.
Mitsubishi recommends that after the 100,000 mile (160,000 km), and on 1989 and later models, 120,000 mile (192,000 km), service is performed, the light bulb be removed from the indicator. This does not relieve the owner from performing needed maintenance; it just turns the light off permanently. Removing the bulb or disabling the system before the specified mileage is a violation of the Federal Automobile Emissions Act.