DTC P1577 BBV Sensor Circuit Low Voltage. Cadillac Concours 1996

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 checks for a vacuum sensor reading which could be caused by an open sensor or an open or shorted 5 volt reference or BBV input circuit. When the PCM detects a brake booster vacuum signal voltage of 0.2 volt (-8 kPa VAC) or less, DTC P1577 will set.

### Conditions for Setting the DTC

#### Test Condition

Test continuously.

#### Failure Condition

Brake booster vacuum reading -8 kPa vacuum or less for 2 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 sensor is open BBV display should read -8 kPa or less. If it does not, then the fault is not present.

2. If the brake booster vacuum sensor is open BBV display should read 82-84 kPa with terminals C and B jumpered together.

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. Turn the key ON.
3. Check the Brake Boost Vac display.

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

-7 kPa

Fault not present. Refer to Diagnostic Aids

Go to Step 3

3

1. Disconnect the BBV sensor connector.
2. Jumper BBV sensor connector terminals B and C together.

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

-7 kPa

Go to Step 13

Go to Step 4

4

1. Remove the jumper.
2. Using DMM J 39200 measure the voltage to ground at BBV sensor connector terminal C.

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

4.5 volts

Go to Step 5

Go to Step 7

5

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C1.
3. Measure the resistance to ground at BBV sensor connector terminal B (harness side).

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

100 ohms

Go to Step 12

Go to Step 6

6 | Measure the resistance between PCM connector C1 terminal 70 and BBV sensor connector terminal B (harness side). Is the resistance the same or less than the value specified? | 5 ohms | Go to Step 15 | Go to Step 11

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 to ground at BBV sensor connector terminal C (harness side).

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

100 ohms

Go to Step 10

Go to Step 8

8 | Measure the resistance between PCM connector C1 terminal 65 and BBV sensor connector terminal C (harness side). Is the resistance the same or less than the value specified? | 5 ohms | Go to Step 15 | Go to Step 9
9 | Repair open in CKT 605. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
10 | Repair short in CKT 605. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
11 | Repair open in CKT 1809. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
12 | Repair short to ground in CKT 1809. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

13

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

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 14

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

15

1. Check 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 16

16 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --