P258C: Vacuum Pump Control Circuit Low
The P258C code indicates that the powertrain control module (PCM) has detected a low voltage condition in the vacuum pump control circuit. This circuit is responsible for controlling the vacuum pump, which provides vacuum for various systems such as brake boost, HVAC actuators, and emission controls. A low voltage signal suggests a short to ground, open circuit, or faulty component, potentially leading to insufficient vacuum and compromised system performance.
01. Most Common Causes
- Faulty vacuum pump relay
- Open or shorted vacuum pump control circuit wiring
- Failed vacuum pump motor
- Corroded or loose electrical connector at vacuum pump
- Defective PCM (rare)
02. Symptoms You Will Notice
- Illuminated Check Engine Light
- Hard brake pedal (reduced brake assist)
- HVAC system malfunction (e.g., poor defrost performance)
- Increased engine load or rough idle
- Possible vacuum leak hissing sound
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data to confirm P258C.
Step 2: Visually inspect vacuum pump connector and wiring for damage, corrosion, or loose connections.
Step 3: Test vacuum pump relay operation using a multimeter or scan tool bidirectional control.
Step 4: Measure voltage at vacuum pump connector with ignition on; should be near battery voltage. If low, check circuit for shorts or opens.
Step 5: If voltage is present and relay works, test vacuum pump motor resistance and operation by applying battery voltage directly.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Low vacuum can cause hard brake pedal and reduced braking assistance, increasing stopping distance and risk of accident.
How much does it cost to fix?▼
Typical repair costs range from $50 to $150 for parts and labor, depending on the root cause (e.g., relay, wiring repair, or pump replacement).