DTC P1578 BBV Sensor Circuit Low Vacuum. 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 Brake Booster Vacuum (BBV) sensor changes resistance based on the vacuum inside the brake booster. This diagnostic test monitors the brake booster vacuum along with the manifold vacuum (calculated from MAP). If the brake booster vacuum is too low for a given manifold vacuum and the brakes are not applied, then the brake booster vacuum signal must be in error and DTC P1578 is set.

### Conditions for Setting the DTC

#### Test Conditions

• | DTCs P0107, P0108, P1106, P1577, and P1602 not set.

• | Engine speed 500 RPM or greater for 20 seconds.

• | Brakes not applied.

• | Barometric pressure 72 kPa or greater.

• | MAP 60 kPa or less.

#### Failure Condition

Brake booster vacuum 5 kPa or less for 16 seconds.

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will not illuminate.

• | The PCM will command a message to be displayed.

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

### Conditions for Clearing the Message/DTC

• | The PCM will turn the message OFF after one run and pass of the diagnostic test.

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

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

• | 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.

### Diagnostic Aids

Manipulate the wire harness while watching the scan tool display looking for opens and shorts.

Reviewing the Failure Rec. may help diagnose an intermittent failure by showing how long ago and under what conditions the DTC set.

### Test Description

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

1. If the brake booster vacuum signal is too low, display will be 5 kPa or less. If it is not, then the signal is not too low and an intermittent problem must be present.

2. Checking for vacuum leaks that are causing the low signal.

3. With the BBV sensor terminals B and C jumpered together, brake booster vacuum should read greater than 81 kPa. If it does not, a wiring problem must be present.

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. Connect the scan tool.
2. Start the engine.
3. Check the Brake Boost Vac display

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

5 kPa

Go to Step 3

Fault not present. Refer to Diagnostic Aids

3 | With engine idling, check vacuum to brake booster with vacuum gage. Is vacuum greater than the value specified? | 14 Hg. (47 kPa) | Go to Step 4 | Go to Step 15

4

1. Turn the key ON, engine OFF.
2. Disconnect BBV sensor connector.
3. Jumper BBV sensor connector terminal B to terminal C (harness side).

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

81 kPa

Go to Step 5

Go to Step 11

5 | Using DMM J 39200 measure voltage to ground on jumper. Is voltage less than the value specified? | 0.5 volts | Go to Step 6 | Go to Step 7

6

1. Remove jumper.
2. Measure voltage to ground at BBV sensor connector terminal C (harness side).

Is voltage the same or more than the value specified?

4.5 volts

Go to Step 9

Go to Step 10

7

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 70 and BBV sensor connector terminal B.

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

5 ohms

Go to Step 13

Go to Step 8

8 | Repair the open or high resistance in CKT 1809. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
9 | Repair short to ground in CKT 1809. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
10 | Repair open or short to ground in CKT 605. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

11

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

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 12

12 | Replace the BBV sensor. Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

13

1. Check the terminal contact at the PCM connector C1 terminals 49, 65 and 70.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 14

14 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
15 | Locate and repair cause of low vacuum at brake booster. Has the repair been performed? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --