See Figure 1
On the 1988 Pick-Up, the major component of the system is the altitude switch which is installed on the right side of the dash panel. This switch senses altitude to the height of 6560 ft. (2000 m). The switch is connected to the ECM and makes the check engine lamp inoperable in case of a rich oxygen sensor error at or above the designated altitude.There is no interaction between the altitude switch and the emission control system and the system does not require adjustment.
On the 1989 and later Amigo and P'Up, a Manifold Absolute Pressure (MAP) sensor is used to measure atmospheric pressure though a vacuum switching valve. The system prevents the vehicle's self-diagnostic system from generating a false rich fuel metering error at altitudes higher than the system's set point.