P0199 OBD2 Code Guide
P0199 is a powertrain diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
Fuel Rail Pressure Sensor Circuit Intermittent (Secondary)
Code P0199 indicates that the Powertrain Control Module (PCM) has detected an intermittent or erratic signal from the secondary fuel rail pressure sensor circuit. This means the sensor's readings are not consistently within the expected range, or the electrical connection is unstable, leading to momentary drops or spikes in the reported pressure. The secondary sensor is typically found in vehicles with dual fuel rails or more complex fuel systems, often in diesel applications or high-performance gasoline engines, providing redundant or additional pressure monitoring. This intermittent fault can cause significant drivability issues, including rough idling, hesitation, stalling, or difficulty starting, as the PCM struggles to maintain optimal fuel delivery.
Code verification standard
P0199 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0199 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0199 diagnostic path
- 1Begin by checking for any other related Diagnostic Trouble Codes (DTCs), especially those pertaining to fuel rail pressure (e.g., P0190-P0198) or other fuel system components. Address any co-occurring codes first, as they might be the root cause of the P0199.
- 2Perform a thorough visual inspection of the secondary fuel rail pressure sensor, its electrical connector, and the entire wiring harness leading to the PCM. Look for signs of physical damage, frayed wires, corrosion on terminals, loose connections, or evidence of rodent damage.
- 3With a professional scan tool, monitor the live data stream for the secondary fuel rail pressure sensor. Observe the pressure readings while the engine is running at various RPMs and also while gently wiggling the sensor's connector and the wiring harness. Look for any sudden, erratic fluctuations, drops, or spikes in the reported pressure that coincide with the wiggling.
- 4Using a digital multimeter, perform voltage and resistance checks on the secondary fuel rail pressure sensor circuit. Test the reference voltage (typically 5V), ground signal, and the sensor's signal wire. Compare your readings to the manufacturer's specifications. An intermittent open or short in the wiring or a faulty sensor will often manifest during these tests.
- 5If accessible and applicable to your vehicle's setup, consider using a mechanical fuel pressure gauge to directly measure the fuel rail pressure. Compare this reading to the live data reported by the scan tool from the secondary sensor. A significant discrepancy, especially an intermittent one, could indicate a faulty sensor or an actual intermittent fuel pressure issue that the sensor is accurately reporting.
Verify before repair
- - Replace the Secondary Fuel Rail Pressure Sensor: If diagnostic tests confirm the sensor itself is providing intermittent or incorrect readings, replacing it is the most direct solution.
- - Repair or Replace Damaged Wiring/Connectors: Address any identified issues with the wiring harness, such as frayed wires, corroded terminals, or loose connections. This might involve splicing in new wire sections or replacing the entire connector.
- - Clean Corroded Electrical Terminals: If corrosion is found on the sensor's connector or the PCM's connector, carefully clean the terminals using an electrical contact cleaner and a small brush to ensure a solid electrical connection.
- - Address Underlying Fuel System Issues: While less common for an intermittent circuit code, if the sensor is accurately reporting intermittent pressure fluctuations due to a failing fuel pump, clogged fuel filter, or faulty fuel pressure regulator, these components would need to be inspected and replaced as necessary.
Vehicle-specific pages to check next
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