In this tutorial, you'll learn what the fuel pump inertia switch does, where it's located, how to reset it, and how to test it on the 2001-2012 3.0L V6 Ford Escape and Mercury Mariner.
Although the inertia switch is designed to cut power to the fuel pump in the event of a major impact. The problem is, it doesn't always take a major crash to trip it. A deep pothole, a sudden jolt, or even a light fender bender can trigger it and leave you with an engine no-start condition.
With the info in this step-by-step guide, you'll be able to quickly figure out if the fuel pump inertia switch is the reason your pump isn't running (and keeping the engine from starting).
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 3.0L V6 Ford Escape: 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012.
- 3.0L V6 Mercury Mariner: 2005, 2006, 2007, 2008, 2009, 2010, 2011.
- 3.0L V6 Mazda Tribute: 2001, 2002, 2003, 2004, 2005, 2006.
NO START DIAGNOSTICS: If you're troubleshooting a no-start or fuel pump issue, be sure to check out the related diagnostic tutorials at the bottom of this page:
It'll help you dig a little deeper if the inertia switch isn't the problem.
What Does The Inertia Switch Do?
The fuel pump inertia switch is a mechanical safety device that's built right into the fuel pump's power circuit. Its entire purpose is cutting power to the fuel pump the instant it senses a serious impact or a severe jolt —without needing any input from the PCM.
- Cutting power on a hard hit —Inside the switch, there's a spring-loaded steel ball being held in place by a small magnet. When your Escape or Mariner takes a strong enough impact, that ball pops loose from its seat, breaking the electrical connection to the pump, and instantly shutting off power.
- Helping prevent fuel-fed fires —By shutting down power to the fuel pump after a collision, the inertia switch keeps fuel from spraying out of a broken fuel line. This reduces the risk of fire under the hood or near the gas tank.
- Staying off until manually reset —Once the switch is triggered, it's not resetting on its own. You (or a tow truck driver) have to press the button down to reset it and get the fuel pump running again.
- Causing a "crank but no-start" condition —If the inertia switch is tripped —whether from a crash, a deep pothole, or even a hard door slam— it's shutting off the fuel pump. The engine will crank, but it's never firing up because fuel isn't making it to the fuel injectors.
Where Is The Inertia Switch Located?
On the 2001–2012 Ford Escape and Mercury Mariner, the fuel pump inertia switch is tucked behind the passenger-side kick panel —that's right below the glove box area, down by the floor. If you pull that trim panel off, you'll expose the inertia switch itself, which is a small black plastic box with a red or white reset button sitting on top.
NOTE: The "kick panel" is the plastic trim panel that runs along the lower side of the footwell, right next to where your feet rest when you're sitting in the passenger seat. It's below the glove box and next to the door.
How Do I Reset The Inertia Switch?
Here's how to reset the fuel pump inertia switch:
- Step 1 —Find the switch: Pull the passenger-side kick panel and expose the small box hiding behind it.
- Step 2 —Check the reset button: Look at the top of the switch. If the red (or white) button is popped up, it's tripped and the fuel pump isn't getting power when you crank the engine.
- Step 3 —Press it back down: Push straight down on the button until it clicks into place. The circuit is now ready to deliver power to the fuel pump.
- Step 4 —Start the engine: With inertia switch reset, the engine should now start. If it doesn't start, then the switch itself wasn't the cause of the engine no-start.
NOTE: If the button is already sitting flush when you first find it, the switch isn't the issue causing the engine to not start.
How To Test The Inertia Switch (Step-By-Step)
Testing the inertia switch —to confirm if it's receiving power (PWR IN) and passing it (PWR OUT) on to the fuel pump— is something you can do with a multimeter or a 12V automotive test light.
Here's how:
- Step 1 —Unplug the switch: Find the inertia switch and disconnect it from its 2-wire electrical connector. One wire is delivers PWR IN from the fuel pump relay and the other carries it (PWR OUT) to the fuel pump.
- Step 2 —Check for PWR IN:
- If you're using a multimeter, set it to Volts DC mode.
- Connect the alligator clip of your 12V test light (or the black multimeter test lead) to a paint-free and rust-free metal spot under the dash.
- With the test light's probe (or red multimeter test lead), probe the terminal that connects to the PWR IN wire.
- Have your helper crank the engine.
- The test light should light up (or the multimeter should display 10 to 12 Volts), indicating the inertia switch is receiving PWR IN.
- If there's no PWR IN, your next step is to check the fuel pump fuse and fuel pump relay.
- NOTE: For the wire color of the PWR IN wire, see: Fuel Pump Inertia Switch Circuit Descriptions.
- Step 3 —Check for PWR OUT:
- Remove the inertia switch (to better access and probe the PWR OUT circuit).
- Reconnect the inertia switch to its 2-wire connector.
- Connect the alligator clip of your 12V test light to a paint-free and rust-free metal spot under the dash.
- Tilt the inertia switch slightly —not too much or it'll trip.
- Backprobe the connector where the PWR OUT wire exits the connector with the test light's probe.
- Have your helper crank the engine.
- The 12V test light should illuminate if the inertia switch is sending power to the fuel pump (or FPDM module). This result also confirms the inertia switch is good.
- Step 4 —Do a bypass test (optional):
- Disconnect the inertia switch from its 2-wire connector.
- With a short jumper wire, connect the two terminals in the pigtail connector.
- Crank the engine.
- If the fuel pump starts running (or the engine starts), it confirms the inertia switch is faulty.
IMPORTANT: Never leave that jumper wire in as a permanent fix. The inertia switch is there as a safety device. If it's bad, replace it. Driving around with the switch bypassed is dangerous —in a crash, the fuel pump will keep running and could turn the accident into a fire. The bypass is only for confirming the diagnosis, not for keeping the vehicle on the road.
Fuel Pump Inertia Switch Circuit Descriptions
The tables below show the wire colors for the two terminals of the fuel pump inertia switch connector across different model years —so you know exactly what to probe when testing for PWR IN and PWR OUT.
| 2001-2004 Escape, And Mariner | |
|---|---|
| Wire | Description |
| Dark green with yellow stripe (DK GRN/YEL) | 12 Volts IN (from Fuel Pump Relay) |
| Pink with black stripe (PNK/BLK) | 12 Volts OUT (to fuel pump) |
| 2005-2007 Escape And Mariner | |
|---|---|
| Wire | Description |
| Light blue with red stripe (LT BLU/RED) | 12 Volts IN (from Fuel Pump Relay) |
| Pink with black stripe (PNK/BLK) | 12 Volts OUT (to fuel pump driver module) |
| 2009-2012 Escape And Mariner | |
|---|---|
| Wire | Description |
| Green with orange stripe (GRN/ORG) | 12 Volts IN (from Fuel Pump Relay) |
| Violet with white stripe (VIO/WHT) | 12 Volts OUT (to fuel pump driver module) |
More Fuel Pump Troubleshooting Help
The inertia switch is only one link in the fuel system chain. If the engine is still cranking but not starting, you'll need to keep looking and checking the rest of the system to see where the problem is hiding.
The following step-by-step tutorials will walk you through testing the fuel pump itself and the Fuel Pump Driver Module (FPDM).
FUEL PUMP PRESSURE TESTS:
FUEL PUMP DRIVER MODULE (FPDM) TESTS:
- Fuel Pump Driver Module Tests (2005-2008 3.0L V6 Ford Escape, Mercury Mariner).
- FPDM Basic Operating Theory (2005-2008 3.0L Ford Escape, Mercury Mariner).
FUEL PUMP AMPERAGE DRAW TEST:
More 3.0L V6 Ford Escape Diagnostic Tutorials
You can find a complete list of 3.0L V6 Ford Escape, Mercury Mariner, and Mazda Tribute diagnostic tutorials in this index:
Here's a sample of the diagnostic tutorials you'll find in the index:
- How To Test The MAF Sensor (2001-2007 Ford 3.0L V6 Ford Escape).
- How To Test Engine Compression (2001-2012 3.0L V6 Ford Escape).
- How To Test For A Blown Head Gasket (2001-2012 3.0L V6 Ford Escape).
- How To Test The Fuel Pump (2001-2004 3.0L Ford Escape).
If this info saved the day, buy me a beer!
