Circuit Description
WARNING: This page is about a different car, the 1998 GMC Forward Control and 1998 Chevrolet Forward Control. However, it is still accessible from the selected car via links, so may be relevant.
Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). A 5-volt reference is applied to sensor. A variable resistor moves in relation to manifold pressure and a voltage signal is returned to VCM through MAP signal circuit. Voltage signal varies from 1.0-1.5 volts at closed throttle (high vacuum) to 4.0-4.5 volts at wide open throttle (low vacuum). A change in throttle position and engine speed should precede change in MAP. If change does not occur, MAP malfunction is present. VCM utilizes MAP signal and throttle position to determine fuel delivery.
Conditions for setting DTC:
- Engine is running.
- No IAC or TP sensor DTCs set.
- No EGR DTCs are set.
- Change in engine speed is less than 75 RPM.
- Change in throttle position is less than 1.5 percent.
- Change in EGR flow is less than 2 percent.
- Change in IAC is less than 4 counts.
- No change in brake switch status.
- No change in clutch status (M/T).
- No change in power steering switch status.
- No change in A/C clutch status.
- Conditions have stabilized for 2 seconds.
- Engine speed between 400-5000 RPM.