Circuit Description
The brake booster pressure sensor measures the negative air pressure or vacuum in the brake booster assembly. The engine control module (ECM) supplies the following circuits to the brake booster pressure sensor:
| • | A 5-volt reference circuit |
| • | A signal circuit |
| • | A low reference circuit |
During engine running conditions, the brake booster pressure sensor signal circuit voltage varies, depending on the vacuum reserve internal to the brake booster. If the ECM detects that the brake booster vacuum is less than the intake manifold vacuum, then DTC P0556 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0556 Brake Booster Pressure Sensor Performance
Conditions for Running the DTC
| • | The engine is running at an idle condition. |
| • | The ignition voltage is greater than 11 volts, but less than 18 volts. |
| • | DTC P0556 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects brake booster vacuum as being less than the intake manifold vacuum for more than 100 milliseconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, last test failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views and Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | Are DTCs P258A, P258B, P258C, P258D, P0557, or P0558 also set? | -- | Go to Step 3 | |
3 |
Does the DTC set during this ignition cycle? | -- | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections |
4 |
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 5 |
5 |
Is the difference between the vacuum gage and the vacuum calculated parameter more than the specified value? | 7 kPa (2 in Hg) | Go to Step 6 | |
6 |
Did the vacuum reading decrease after 30 seconds? | -- | Go to Step 15 | Go to Step 7 |
7 |
Is the difference between the Mityvac Gage display and the brake booster pressure sensor parameter more than the specified value? | 7 kPa (2 in Hg) | Go to Step 8 | Go to Testing for Intermittent Conditions and Poor Connections |
8 |
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 9 |
9 | Measure the resistance of the 5-volt reference circuit between the ECM electrical connector and the brake booster pressure sensor electrical connector. Refer to Circuit Testing . Does the resistance measure greater than the specified value? | 2 ohms | Go to Step 12 | Go to Step 10 |
10 | Measure the resistance of the signal circuit between the ECM electrical connector and the brake booster pressure sensor electrical connector. Refer to Circuit Testing . Does the resistance measure greater than the specified value? | 2 ohms | Go to Step 13 | Go to Step 11 |
11 | Measure the resistance of the low reference circuit between the ECM electrical connector and the brake booster pressure sensor electrical connector. Refer to Circuit Testing . Does the resistance measure greater than the specified value? | 2 ohms | Go to Step 14 | Go to Step 16 |
12 | Repair the high resistance in the 5-volt reference circuit of the brake booster pressure sensor. Refer to Wiring Repairs . Did you complete the repairs? | -- | Go to Step 17 | -- |
13 | Repair the high resistance in the signal circuit of the brake booster pressure sensor. Refer to Wiring Repairs . Did you complete the repairs? | -- | Go to Step 17 | -- |
14 | Repair the high resistance in the low reference circuit of the brake booster pressure sensor. Refer to Wiring Repairs . Did you complete the repairs? | -- | Go to Step 17 | -- |
15 | Replace the brake booster pressure sensor. Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
