DTC P1108 BARO to MAP Sensor Comparison Too High. Cadillac Concours 1997

For 1990-2009 cars
Engine Controls Components
IAT/ ECT/ TP/ MAP and BBV Sensors
OBD II Symbol Description Notice
ESD Notice
ESD Notice

### Circuit Description

The Manifold Absolute Pressure (MAP) sensor is a sensor that changes resistance based upon manifold vacuum. The PCM provides a 5 volt reference and ground. The MAP sensor signal varies between ground and 5 volts as manifold vacuum varies. As MAP decreases, voltage decreases (low engine load, high vacuum). As MAP increases, voltage increases (high engine load, low vacuum). The PCM uses the MAP sensor values as an indicator of engine load. This diagnostic test monitors the MAP signal by comparing the reading to calculated BARO. If the values of the MAP signal and the calculated BARO are too close together at idle, DTC P1108 sets.

### Conditions for Setting the DTC

#### Test Conditions

• | DTCs P0107, P0108, P0122, P0123, not set.

• | Throttle position at idle ,calculated by the PCM.

• | TP sensor 18 degrees or less.

• | Engine speed 400 RPM or greater.

• | Barometric pressure 75 kPa or greater.

#### Failure Condition

Difference between MAP and Calculated BARO is 11 kPa or less for 15 seconds.

### Action Taken When the DTC Sets

• | PCM disables long term fuel trim.

• | PCM uses a substitute MAP value based on engine RPM and throttle angle.

• | PCM uses 92.2 kPa for barometric pressure.

• | PCM disables Evaporative Emission (EVAP) control solenoid.

• | PCM disables torque management.

• | Transaxle shift adapts are maintained at current levels.

• | The PCM will illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

• | A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

• | A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.

• | Use a scan tool to clear DTCs.

• | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. MAP at idle should be 30-50 kPa, depending on engine load. BARO should be 85 to 105 kPa, depending on altitude. The difference between the two should always be greater than 11 kPa with the engine running at or near idle.

2. Check for vacuum at the throttle body with a vacuum gage. At idle, typical vacuum readings are 14-20 Hg, depending on engine load.

3. MAP display should read 10-16 kPa disconnected.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to A Powertrain On Board Diagnostic (OBD) System Check

2

1. Start and idle the engine.
2. Using a scan tool view the MAP and BARO displays.
3. Subtract MAP value from BARO value.

Is difference between BARO and MAP values the same or less than the value specified?

11 kPa

Go to Step 3

Fault not present. Go to DTC P0106 Manifold Absolute Pressure (MAP) System Performance

3 | With engine idling, check engine vacuum with a vacuum gage at the MAP sensor port. Does vacuum measure greater than the value specified? | 14 Hg (47 kPa) | Go to Step 4 | Go to Step 14

4

1. Turn the key to LOCK.
2. Disconnect the MAP sensor connector.
3. Key ON, engine OFF.
4. Check the MAP display.

Is the display the same or less than the value specified?

16 kPa

Go to Step 5

Go to Step 7

5 | Using DMM J 39200 measure the voltage to ground at MAP sensor connector terminal C. Is the voltage less than the value specified? | 5.5 volts | Go to Step 6 | Go to Step 12

6

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C1.
3. Measure the resistance between PCM connector C1 terminal 46 and MAP sensor connector terminal A.

Is the resistance the same or less than the value specified?

5 ohms

Go to Step 11

Go to Step 9

7

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C1.
3. Turn the key ON.
4. Using DMM J 39200 measure the voltage to ground at MAP sensor connector terminal B (harness side).

Is the voltage the same or less than the value specified?

0.5 volts

Go to Step 10

Go to Step 8

8 | Repair short to voltage on the MAP Sensor Signal circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
9 | Repair open in the MAP Sensor Ground circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

10

1. Check terminal contact at the PCM connector C1 terminals 46, 64 and 69.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 15

11

1. Check terminal contact at the MAP sensor.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 13

12 | Repair short to voltage on the 5 Volt Reference circuit of the MAP or TP Sensor. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
13 | Replace the MAP sensor. Refer to MAP Sensor Replacement . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
14 | Check and repair causes of intake manifold vacuum leaks or low engine vacuum. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
15 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --