Jetta Fuel Pump Relay Problemsby Pat Martin
Your Jetta has two fuel pumps. One is in the gas tank, and the main fuel pump is under the car. If your Jetta will not start or stay running, your powertrain may record fuel pump fault codes of P0230 to P0233. A scanner attached to your powertrain wiring system can read these diagnostic codes that can tell you if the problem is mechanical or electrical in nature.
Locate the Problem
Fuel injection systems are sensitive to fuel volume and fuel pressure. Though most cars require 30 to 80 pounds per square inch of fuel pressure, 29 or 81 pounds per square inch will cause the fuel pump to fail. The fuel pump circuit includes an oil pressure solenoid and an inertia switch, which is activated during accidents. The inertia or safety switch in new vehicles turns off the fuel pump if a hard jolt or accident occurs. The safety switch turns off the fuel pump if a fuel line leaks, even minutely. The fuel pump may need to be reset manually if the safety switch has been activated.
Check Engine Light
If the "Check Engine" light is on, your engine's emissions level is too high. The "Check Engine" light most likely means that the fuel system is not properly pressurized, or the gasoline/air mixture is incorrect. If the powertrain diagnostic code is P0452, the fuel tank pressure sensor is reporting that the voltage is low on the fuel tank pressure circuit. A Fuel Tank Pressure Transducer (FTPT), a Canister Vent Solenoid (CVS) and Fuel Level Input (FLI), along with a Canister Purge Valve (CPV), can be used to find fuel leaks 0.040-inch in diameter or larger. Federal law requires vehicles to have less than a 0.040-inch leak rather while the California standard is a 0.020-inch leak. Some vehicles may run a 0.090/0.020-inch detection configuration and turn the 0.040-inch leak test off as provided for in the regulations. In the case of heavy-duty gasoline engines, regulations require 0.150-inch leak detection only.
Fuel Pump Relay Function
Turning the key in the ignition sends an impulse to the Powertrain Control Unit (PCU), which activates the fuel pump relay to start the fuel pump motor. The fuel pump pressurizes the fuel system before the engine starts. Fuel enters the fuel pump through a filtered tube and exits the pump by a one-way valve. The fuel pump runs continuously once the engine starts and does not stop until the ignition key is switched off. The PCU signals the fuel pump to quit if it does not receive an RPM signal from the PCU. A fuel pump that will not start at all could be due to a clogged fuel filter or the fuel pump relay.
Faulty Fuel Pump Relay
If the fuel pump runs and the fuel pressure is normal, but the engine will not start, the problem is the fuel pump relay. The fuel pump does not pump enough gas if the voltage to it is low. Voltage to the fuel pump must be within half a volt of normal. A fuel pump that creates normal pressure but does not inject enough fuel can be tested with a fuel gauge or by disconnecting the fuel lines and running a line into a container. Remember that gasoline is highly flammable. Make sure it is not near any sparks. A good fuel pump delivers a quart of fuel every 30 seconds.
Pat Martin has been writing nonfiction since 1978. Her articles have appeared in the “Nautical Research Guild Journal” and the “Worcester County Times,” among other publications. Martin is a National Board certified professional counselor and holds a Master of Science in human services from Capella University.