Power Window Fuse and Relay Test for Windows That Go Down but Not Up

Windows that roll down fine but refuse to come back up are more than just annoying they can leave your car exposed to weather, theft, or a failed state inspection. Add a check engine light for the catalytic converter into the mix, and you've got two problems that seem unrelated but sometimes share a common electrical root cause. Testing your power window fuse and relay is the first place to start because these components control the flow of electricity to your window motor, and a weak or failed relay or blown fuse can cause exactly this kind of one-direction operation. Here's how to figure out what's going on and fix it.

Why would my window go down but not back up?

Power window systems use a reversible motor. When you press the switch down, current flows one direction through the motor. When you press up, it reverses. A fuse protects the circuit, and a relay (in some vehicles) helps manage the higher current needed to move the glass.

If the window goes down but won't go up, the problem usually falls into one of these categories:

Blown fuse Some vehicles use separate fuses for the up and down circuits, or a single fuse that partially fails under load in one direction.
Faulty window relay The relay may click and allow current in one direction but fail to energize for the reverse direction.
Worn window motor brushes Brushes inside the motor can wear unevenly, allowing rotation in one direction but not enough torque in the other.
Bad window switch contacts The "up" side of the switch may have burned or corroded contacts.
Wiring issue A corroded or broken wire on the up-circuit side can block current from reaching the motor.

If you're noticing this symptom alongside a catalytic converter check engine light, there's a chance the two are connected through a shared fuse or ground point, especially in vehicles where interior electrical systems and emissions monitors share a fuse box circuit. For a deeper look at how a blown fuse can cause one-direction window operation, see these symptoms of a blown fuse causing one-way window operation with a catalytic converter warning.

Could the check engine light for the catalytic converter be related to the window problem?

At first glance, a catalytic converter code (like P0420 or P0430) and a stuck power window seem like completely separate issues. In most cases, they are. But there are exceptions:

Shared fuse panel circuits Some vehicle manufacturers route circuits for interior accessories and emissions sensors through the same fuse block. A short or overload in one circuit can blow or weaken a fuse that feeds another.
Low voltage from a failing alternator or weak battery If the charging system isn't keeping up, the engine control module (ECM) may throw a catalyst efficiency code due to erratic sensor readings, while the window motor gets just enough voltage to roll down (low load) but not enough to push the glass up (higher load against gravity).
Shared ground point Corrosion at a common ground can cause erratic behavior across unrelated systems.

A mechanic can check whether both systems share a fuse, relay, or ground path by looking at the vehicle's wiring diagram. Don't assume they're connected but don't rule it out either.

What tools do I need to test the power window fuse and relay?

You don't need expensive equipment. Here's what helps:

Test light or multimeter A 12V test light is the quickest way to check for power. A multimeter gives more precise voltage readings and can test continuity.
Fuse puller or needle-nose pliers To remove fuses without damaging them.
Vehicle owner's manual Identifies fuse and relay locations specific to your car.
Jumper wire or relay tester To bench-test or bypass a suspect relay.

How do I test the power window fuse step by step?

Locate the fuse box. Most cars have one under the dashboard on the driver's side and another under the hood. The owner's manual or the fuse box cover diagram will point you to the power window fuse it's often labeled "P/W," "WDO," or "Power Window."
Inspect the fuse visually. Pull it out and look at the metal strip inside. If it's broken or blackened, the fuse is blown. On mini fuses, hold it up to light the thin metal bridge should be intact from end to end.
Test with a multimeter. Set the multimeter to continuity mode (the symbol that looks like a sound wave). Touch one probe to each metal tab on the fuse. A good fuse will beep or show near-zero resistance. No beep means the fuse is open and needs replacement.
Check voltage across the fuse slot. With the key on, touch the test light or multimeter probes to both fuse slots in the box. You should see 12V on both sides. If one side shows 12V and the other shows 0V, the fuse is blown.
Replace with the same amperage. Never upsize a fuse. If a 20A fuse keeps blowing, there's a short circuit downstream that needs to be found and fixed.

If the fuse checks out fine, move on to the relay. If you notice a blown fuse is part of a broader pattern, you might find it helpful to review common symptoms where a blown fuse causes one-way window operation alongside a catalytic converter warning.

How do I test the power window relay?

Not all vehicles have a dedicated power window relay many older systems run the window motor directly through the switch. But if your car does use a relay, here's how to test it:

Find the relay. Check the fuse box diagram. It may be labeled "P/W Relay" or "Window Relay."
Listen for a click. With the key on, press the window switch (up and down). You should hear or feel the relay click each time. No click on the "up" position but a click on "down" points to a relay or switch problem on that circuit.
Swap it with a known good relay. Many vehicles use the same relay type for multiple systems (horn, A/C compressor, etc.). Swap the window relay with an identical one from another circuit. If the window now works in both directions, you've found the problem.
Test with a multimeter. Remove the relay and check resistance between the coil pins (usually pins 85 and 86). A good relay coil reads roughly 50–120 ohms. Between the switch pins (usually 30 and 87), you should see open circuit with no power applied. Apply 12V to the coil pins you should hear a click, and pins 30 and 87 should show continuity.
Check for corrosion. Pull the relay out and look at the pins and socket. Green or white corrosion can create enough resistance to prevent the relay from working in one direction under load.

For a more detailed walkthrough on diagnosing a bad window relay after catalytic converter work, see this guide on bad window relay diagnosis when the motor works in one direction only.

What are common mistakes when testing window fuses and relays?

Checking only one fuse box. The window circuit may use more than one fuse across different boxes. Check both the interior and under-hood fuse panels.
Assuming the fuse is good because it looks fine. A fuse can fail internally without obvious visual damage. Always test with a multimeter or test light.
Ignoring voltage drop. A fuse or relay can pass a basic continuity test but still cause problems if there's resistance at the contacts. Test under load if possible.
Replacing the motor before testing simpler parts. Fuses and relays cost a few dollars and take minutes to test. A window motor costs much more and takes longer to replace. Always start cheap and simple.
Clearing the check engine light without diagnosing it. If the catalytic converter code keeps coming back, it's a real problem not just a glitch. Address it separately so it doesn't mask other electrical issues.

When should I check the window motor or switch instead?

If your fuse and relay both test good, the next steps are:

Test for power at the motor connector. Disconnect the motor plug, set your multimeter to DC volts, press the "up" button, and check for 12V at the connector. If you see 12V but the motor doesn't run, the motor is bad. If you don't see voltage, the problem is between the switch and the motor (wiring, relay, or switch).
Test the switch. With the switch plugged in, back-probe the connector with a multimeter. The switch should send 12V to the motor on both "up" and "down" inputs. If the "up" side shows no voltage, the switch contacts are worn or burned.
Check for a binding regulator. Sometimes the window regulator (the mechanical track and cable system) is sticking. The motor gets power and tries to work but can't overcome the friction. This feels different from an electrical failure you might hear the motor straining. Lubricate the tracks with silicone spray as a first step.

Quick checklist before you start

☐ Find the correct fuse location using your owner's manual or fuse box cover diagram
☐ Test the power window fuse with a multimeter (continuity and voltage)
☐ Check for corrosion in the fuse socket
☐ Test or swap the power window relay with an identical one
☐ Confirm 12V reaches the window motor connector on the "up" circuit
☐ Rule out a binding window regulator before condemning the motor
☐ Diagnose the catalytic converter code separately pull the code, check for a shared fuse or ground, and fix the emissions issue
☐ If both problems share a circuit, repair that root cause and retest both systems

Tip: If you replaced a catalytic converter recently and the window problem started right after, double-check that no fuses were blown during the repair and that all ground straps were reconnected. Welding or disconnecting the battery during exhaust work can sometimes pop fuses or cause the body control module to lose its settings, leading to odd electrical behavior in unrelated systems. Always pull diagnostic trouble codes with an OBD-II scanner after any major repair a P0420 catalytic converter code and a window malfunction together may point to a deeper electrical issue worth professional diagnosis.