Component Testing

Erratic Signal Test

1. Turn ON the ignition, with the engine OFF, and remove the B74 MAP sensor.
2. Install a 3 A fused jumper wire between the 5 V reference circuit terminal 1 and the corresponding terminal of the B74 MAP sensor.
3. Install a jumper wire between the low reference circuit terminal 2 of the MAP sensor and ground.
4. Install a jumper wire at the MAP sensor signal circuit terminal 3.
5. Connect a DMM between the jumper wire from the MAP sensor signal circuit and ground.
6. Install the J 35555:  Metal Mityvac to the MAP sensor vacuum port. Slowly apply vacuum to the sensor while observing the voltage on the DMM. The voltage should vary between 0-5.2 V without any spikes or dropouts.
   • If the voltage is not within the specified range or is erratic, replace the B74 MAP sensor.

Skewed Sensor Test

1. Using the following steps and referencing the table below will determine if the MAP sensor is skewed.
2. Ignition ON, engine OFF, observe the MAP Sensor scan tool parameter.
3. Use the observed MAP Sensor scan tool parameter that is closest to a value that is indicated in the first column.

   THEN

4. Using the J 23738:  Mityvac or the J 35555:  Metal Mityvac to apply 5 in Hg of vacuum to the B74 MAP sensor, the parameter in the first column should decrease by 17 kPa (2.5 psi). The acceptable range is indicated in the second column.
5. Using the J 23738:  Mityvac or the J 35555:  Metal Mityvac to apply 10 in Hg of vacuum to the B74 MAP sensor, the parameter in the first column should decrease by 34 kPa (4.9 psi). The acceptable range is indicated in the third column.
   • If not within the specified range, replace the MAP sensor.