The BARO (Barometric Pressure) sensor is a variable capacitance sensor that, when supplied with a 5 volt reference signal from the ECM, produces a linear analog voltage signal that indicates pressure.
For the Barometric Pressure Sensor function diagram, See Figure
“Barometric Pressure Sensor Function Diagram”
.
Figure 1. Barometric Pressure Sensor Function Diagram
Timing Control — The BARO signal is used to determine altitude to adjust the timing and fuel quantity to optimize engine operation and control smoke throughout all altitude conditions.
Section 17.1.1
Fault Detection Management
A BARO signal that is detected out of range high or low by the ECM will cause the ECM to ignore the BARO signal and use the MAP (Manifold Absolute Pressure) signal generated at low idle as an indication of barometric pressure. If a MAP fault is also detected, the BARO will default to 29.6 in. Hg of barometric pressure. See Figure
“Recommended Wiring for the Barometric Air Pressure Sensor”
.
Figure 2. Recommended Wiring for the Barometric Air Pressure Sensor
Connector voltage checks are listed in Table
“Connector Voltage Checks”
. Check with the sensor connector 406 disconnected, the ignition key ON and all accessories OFF.
| Test Points | Spec | Comments |
| 1 to Grd | < 0.25v | If voltage is greater than 0.25v signal wire is shorted to VREF or battery. |
| 2 to Grd | 5 ± 0.5 volts | VREF, check with key ON; if voltage not in spec, see VREF circuit. |
| 2 to Grd | < 0.25v | If voltage is greater than 0.25v, signal wire is shorted to VREF or battery. |
Connector checks to chassis ground are listed in Table
“Connector Checks to Chassis Ground”
. Check with the sensor connector 406 disconnected, the positive battery cable disconnected and the ignition key OFF.
| Test Points | Spec | Comments |
| 1 to Grd | < 5 Ω | Resistance to chassis ground, check with key off; > 5 Ω, the harness is open. |
| 2 to Grd | > 1,000 Ω | Resistance less than 1,000 Ω indicates a short to ground. |
| 3 to Grd | > 1,000 Ω | Resistance less than 1,000 Ω indicates a short to ground. |
Harness resistance checks are listed in Table
“Harness Resistance Checks”
. Check with the breakout box installed on the chassis harness only.
| Test Points | Spec | Comments |
| #11 to 1 | < 5 Ω | Resistance from sensor connector to 60-pin connector – signal ground |
| #3 to 2 | < 5 Ω | Resistance from sensor connector to 60-pin connector – VREF |
| #29 to 3 | < 5 Ω | Resistance from sensor connector to 60-pin connector – BARO signal |
Operational voltage checks are listed in Table
“Operational Voltage Checks”
. The test points are + No. 29 to —No. 11. Check with the breakout box installed in line with the ECM.
| Voltage | In. Hg | kPa | Comments |
| 4.89 | 31.0905 | 105 | High atmospheric pressure |
| 44.60 | 29.61 | 100 | Normal atmospheric pressure at sea level |
| 2.60 | 17.766 | 60 | Normal atmospheric pressure at 10,000 feet |
Fault code descriptions are listed in Table
“Fault Codes”
.
| Fault Code | Description |
| 151 | Signal voltage was greater than 4.95 volts for more than 1.0 seconds. |
| 152 | Signal voltage was less than 1.0 volts for more than 1.0 seconds. |
Section 17.1.2
Barometric Pressure Sensor Operation
The ECM sends a regulated 5 volt signal from the ECM (black) chassis connector terminal 3 to the BARO connector terminal 2. The BARO sensor returns a variable voltage signal (represents atmospheric pressure) from the BARO connector terminal 3 to the ECM at terminal 29. The BARO sensor is grounded from the BARO connector terminal 1 to the ECM signal ground terminal 11.
Section 17.1.3
ECM Diagnostics
The ECM continuously monitors the signal from the BARO sensor to the ECM terminal 29. If the signal is out of the expected range, a fault is logged (warning light does NOT turn on) and the ECM uses the MAP signal generated at low idle to determine barometric pressure.
Section 17.1.4
Flash Codes
Flash Code 151
ATA Code PID 108 FMI 3
ECM: BARO signal out of range high; the BARO signal is greater than 34.95 volts for more than one second.
Flash Code 152
ATA Code PID 108 FMI 4
ECM: BARO signal out of range low; the BARO signal is less than 1.0 volt for more than one second.
| Series 40E Troubleshooting Manual – 6SE241 |
| Generated on 10-13-2008 |