1994 PCED OBDI-A
SECTION 18A: Diesel Diagnosis — 7.3L DI Engine
AC: Barometric Pressure (BARO) Sensor
Introduction
  AC: Pinpoint Tests  
Signal Functions

The BARO (barometric pressure) sensor is a variable capacitance sensor that when supplied with a 5-volt reference signal from the PCM produces a linear analog voltage signal that indicates pressure.

Timing Control — The BARO signal is used to determine altitude to adjust timing and fuel quantity to optimize engine operation and control smoke throughout all altitude conditions.

Glow Plug Control — The BARO signal (barometric pressure) is one of the variables used to calculate glow plug on time. At higher altitudes glow plug on time is increased to insure faster clean up of start-up smoke.





Detection/Management

A BARO signal that is detected out of range high or low by the PCM will cause the PCM to ignore the BARO signal and use the MAP signal generated at low idle as an indication of barometric pressure.





Note

After removing connectors always check for damaged pins, corrosion, loose terminals etc.



Connector Checks to Ground (B-)
(Check with sensor connector disconnected and ignition key off, all accessories off)
Test PointsSpec.ActualComments
A to Grd<5 ohms Resistance to chassis ground check with key off. If greater than 5 ohms the harness is open.
B to Grd>5 ohms Resistance less than 5 ohms indicates a short to ground.
C to Grd>5 ohms Resistance less than 5 ohms indicates a short to ground.



Connector Voltage Checks
(Check with sensor connector disconnected and ignition key on)
Test PointsSpec.ActualComments
A to Grd0-.25 volt If greater than .25 volts signal wire is shorted to VREF or battery.
B to Grd5 volts VREF signal should be 5 volts ± 0.1 volt.
C to Grd0-.25 volt Signal voltage. If greater than .25 volts shorted to VREF or battery.



Harness Resistance Checks
(Check with breakout box installed on engine harness only)
Test PointsSpec.ActualComments
No. 91 to A<5 ohms Resistance from sensor connector to 104 pin connector.
No. 90 to B<5 ohms Resistance from sensor connector to 104 pin connector.
No. 84 to C<5 ohms Resistance from sensor connector to 104 pin connector.



Test Points (+) No. 84 to (-) No. 91Operational Signal Checks
(Check with breakout box installed in line with the PCM)
VoltagePSIKPAActualComments
 00 Voltage with key on engine off, atmospheric pressure

DTC Descriptions

Circuit Faults:

827 = Signal voltage was less than .04 volts.

828 = Signal voltage was greater then 4.90 volts.

 

 

  AC: Pinpoint Tests