Barometric Pressure (BARO) Sensor

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 barometric pressure.

Timing Control

The BARO signal if 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 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 startup smoke.

Fault 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 Manifold Absolute Pressure (MAP) signal sensed at low idle as an indication of barometric pressure. If the MAP signal has also failed, a fixed value of 29.61 In. Hg. (14.6 PSI) is used as the default. The NGS tool will display the PID default value of 29.61 In. Hg. (14.6 PSI) when the BARO system has failed.

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 Points	Spec	Comments
(1) to Grd.	< 5 ohms	Resistance to chassis grd, check w/key off, > than 5 ohms the harness is open.
(2) to Grd.	> 1000 ohms	Resistance less than 1000 ohms indicates a short to ground.
(3) to Grd.	> 1000 ohms	Resistance less than 1000 ohms indicates a short to ground.

Connector Voltage Checks (Check with Sensor Connector Disconnected and Ignition Key On)

Test Points	Spec.	Comments
(1) to Grd.	0 - .25 volts	If greater than .25 volts signal wire is shorted to VRef or battery.
(2) to Grd.	5 Volts ± .5	VRef check with key ON, if voltage is not spec., see VRef circuit
(3 ) to Grd.	0 - .25 volts	If greater than .25 volts signal wire is shorted to VRef or battery.

Harness Resistance Checks (Check with breakout box installed on engine harness only)

Test Points	Spec	Comments
#91 to (1)	< 5 ohms	Resistance from sensor connector to 104 pin connector - Signal Ground
#90 to (2)	< 5 ohms	Resistance from sensor connector to 104 pin connector - VRef
#84 to (3)	< 5 ohms	Resistance from sensor connector to 104 pin connector - BARO signal

Operational Voltage Checks (Check with breakout box installed in line with the PCM)

Test Points (+) #84 to (-) #91		kPa	Comments
Voltage	In. Hg.
4.89	31.0905	105	High atmospheric pressure
4.6	29.61	100	Normal atmospheric pressure at sea level
2.6	17.766	60	Normal atmospheric pressure at 10,000 feet

Diagnostic Trouble Code Descriptions

0108 = Signal voltage was greater than 4.9 volts for more than .2 seconds
0107 = Signal voltage was less than .04 volts for more than .2 seconds