What Does P0559 Mean?
The ECM has detected intermittent signal behavior from the brake booster pressure sensor circuit. The sensor signal exhibits momentary spikes, dropouts, or erratic behavior that does not correspond to actual brake booster pressure changes. This intermittent condition is distinct from a steady fault and typically points to a loose connection or damaged wiring that fails under vibration or temperature changes.
Safety Warning
An intermittent brake booster pressure signal can cause unpredictable behavior of brake assist features. The ECM may intermittently enable or disable vacuum management and hill-start assist, leading to inconsistent braking feel.
Common Causes
40%
Loose or worn brake booster pressure sensor connector with intermittent terminal contact during engine vibration or vehicle motion
25%
Intermittent break in the sensor wiring harness at a stress point or flex area
25%
Failing brake booster pressure sensor with intermittent internal connection from thermal cycling
10%
Corroded ECM connector pin on the brake booster pressure sensor input making intermittent contact
Diagnostic Steps
1
Step 1: Monitor the brake booster pressure sensor live data at idle. The reading should be steady at the current vacuum level. Any sudden spikes or dropouts confirm the intermittent condition.
2
Step 2: Perform a wiggle test on the sensor connector, each wire in the harness, and the ECM connector while monitoring live data. Note which manipulation causes signal disturbance to pinpoint the fault location.
3
Step 3: Inspect the sensor connector for signs of moisture intrusion, corroded terminals, or loose pin retention. Check that the connector locks securely.
4
Step 4: Trace the wiring harness from the sensor to the ECM, looking for cracked insulation, pinch points, or loose harness mounting clips that allow excessive wire movement.
5
Step 5: If no wiring fault is reproducible during wiggle testing, replace the brake booster pressure sensor as it likely has an intermittent internal failure. Clear codes and verify stable readings under various driving conditions.
Estimated Repair Cost
$60 - $300
Parts + labor, varies by vehicle and location
The ECM has detected intermittent signal behavior from the brake booster pressure sensor circuit. The sensor signal exhibits momentary spikes, dropouts, or erratic behavior that does not correspond to actual brake booster pressure changes. This intermittent condition is distinct from a steady fault ...
The most common cause of P0559 (Brake Booster Pressure Sensor Circuit Intermittent) is: Loose or worn brake booster pressure sensor connector with intermittent terminal contact during engine vibration or vehicle motion
Typical repair costs for P0559 range from $60 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An intermittent brake booster pressure signal can cause unpredictable behavior of brake assist features. The ECM may intermittently enable or disable vacuum management and hill-start assist, leading to inconsistent braking feel.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0559 to identify the root cause.
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Quick Info
Category
Powertrain
System
Brake Assist / Brake Booster System
Difficulty
Type
Generic (SAE)
Recommended Tools
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