Where is the glow plug relay on a 2009 Ford S Max?

The glow plug relay on a 2009 Ford S-Max is usually located in the engine bay’s main fuse/relay box, and you’ll typically find a small rectangular relay labeled Glow, GLW, or GLOW among the other engine relays.

Where to look in the engine bay

To help you locate it quickly, check these common spots and cues in the engine bay of a 2009 S-Max with a diesel engine.

• Inside the engine bay fuse/relay box (the large black plastic box near the battery), among the other relays.


• On some vehicles, the glow plug relay is clearly labeled on the lid of the fuse box; look for markings such as GLOW, GLW, GP, or similar.


• In certain trims or revision years, the glow plug control may be integrated with the engine control unit (ECU) or another control module, meaning there is no separate standalone relay in the box.

If you’re unsure, consult the owner’s manual or a workshop manual for the exact fuse/relay diagram for your VIN, as labeling can vary by engine variant and market specifications.

Labels to look for

Familiarize yourself with common labels you might see on or near the relay: GLOW, GLW, GP, or similar abbreviations indicating the glow plug circuit.

How to confirm and test the glow plug relay

Before testing, ensure you follow safety precautions: the glow system involves high current and hot components; do not touch wiring while the system is energized.

• Check the relevant fuse in the engine bay fuse box to ensure the glow plug circuit is protected and not blown.


• With the ignition in the on position (the glow cycle), listen for a faint relay click from the under-hood fuse box as the glow plugs energize.


• If you have a multimeter and the knowledge to use it safely, test for voltage at the glow plug connectors when the ignition is on; a lack of voltage suggests a faulty relay or wiring issue.


• Inspect the relay and wiring for signs of damage, corrosion, or melted insulation, which can indicate a failing relay or poor connections.

Conclusion: If the relay does not engage, or the glow plugs do not heat during cold starts, the relay or its circuit is a likely fault and should be tested further or replaced by a qualified technician.

What to do if the relay is faulty

Faulty glow plug relays are a common reason for hard starts in cold weather on older diesels. If you suspect a bad relay, consider these steps while keeping safety in mind.

• Obtain the correct replacement relay for your engine variant and VIN, as labeling and part numbers can differ between markets.


• Disconnect the battery before handling electrical components to avoid short circuits.


• Replace the old relay with the new one, reseat all connections, and then recheck the glow cycle with the ignition on.


• If symptoms persist after replacement, have the glow plugs themselves and related wiring tested, as multiple faults can produce similar starting issues.

Note: Glow plug systems are critical for cold-start performance. If you’re not comfortable performing electrical tests or replacement, seek assistance from a qualified mechanic or Ford technician.

Summary

In most 2009 Ford S-Max diesel versions, the glow plug relay lives in the engine bay’s main fuse/relay box and is labeled GLOW, GLW, or similar. If you don’t find a standalone relay, the glow control may be integrated with the ECU or another module. Always consult the vehicle’s fuse diagram for your exact engine variant, and if in doubt, contact a professional to avoid misidentifying components or miswiring the system.

Where are the glow plugs on a Ford S Max?

The glow plugs on the 2.0-liter engine are located at the back of the engine, as illustrated in the image below.

How to check a glow plug relay?

You can test a glow plug relay using a multimeter to perform a resistance test or a voltage drop test. For a resistance test, check for continuity across the relay terminals with the relay removed. For a voltage drop test, measure the voltage across the relay terminals while the system is engaged; the voltage should drop to near zero. 
This video demonstrates how to test a glow plug relay using a multimeter: 57sCamerons on CameraYouTube · Dec 11, 2021
Resistance test

1. Disconnect the relay: from its socket. 
2. Set your multimeter: to the continuity or resistance setting. 
3. Place the multimeter probes: on the relay terminals. For a typical relay, this would be pins 85 and 86, or the input/output terminals. 
4. Interpret the results:
   • If the relay is good, the multimeter should show continuity (a low resistance reading between 50 and 200 ohms is a common range). 
   • If the relay is bad, there will be no continuity or an open circuit reading. 

Voltage drop test

1. Connect your multimeter's black lead: to the ground side of the glow plug relay's output terminals. 
2. Connect the red lead: of the multimeter to the battery's positive terminal. 
3. Turn the ignition on . The multimeter should initially show a reading close to the battery's voltage, such as 12.512.512.5 volts. 
4. Crank the engine . While cranking, the voltage reading on the multimeter should drop to less than 0.50.50.5 volts. A reading higher than this indicates excessive resistance and a faulty relay. 
5. Interpret the results:
   • If the voltage drops to near zero, the relay is likely working correctly. 
   • If the voltage stays high, the relay is not closing its internal contacts properly and is faulty. 

You can watch this video to see how to perform a voltage drop test on a glow plug relay: 58sThe Auto RulesYouTube · Aug 19, 2014
Quick check with a test light 

1. Connect the clamp of a test light: to the positive battery terminal. 
2. With the ignition on, touch the test light probe to the output terminal of the relay (where the wires to the glow plugs connect). 
3. Interpret the results:
   • If the test light glows brightly, it indicates voltage is reaching the glow plugs. 
   • If the test light remains dim or does not light up, the relay is likely bad. 

You can watch this video to learn how to use a test light to check the glow plug relay: 52sthomas brianYouTube · Jan 9, 2021

What is a common fault with Ford S-Max?

Ford S-Max: steering and braking problems
The brakes can wear prematurely, especially the rear brake discs and pads. To avoid these problems, it is important to regularly check and maintain the steering and brakes. Replacement of defective parts and adjustment of the steering may be necessary.

What are the symptoms of a faulty glow plug relay?

Symptoms of a bad glow plug relay include hard starting, especially in cold weather, rough idling or misfiring, white smoke from the exhaust, and a lit-up check engine light. The relay can also make a rapid clicking sound or fail to heat the glow plugs, leading to poor engine performance. 
Common symptoms of a bad glow plug relay

• Hard starting: The engine cranks but takes longer than usual to start, particularly in cold conditions. 
• Rough idling and misfiring: The engine may shake or misfire when it is running. 
• White smoke from the exhaust: This occurs when uncombusted fuel is expelled due to poor heating by the glow plugs, and it often clears up as the engine warms up. 
• Check engine light: A malfunctioning glow plug relay can trigger the check engine light on the dashboard. 
• Poor engine performance: This includes weak acceleration and decreased fuel efficiency. 
• Rapid clicking sound: The relay itself may make a rapid clicking noise. 
• No start: A complete failure of the relay can prevent the vehicle from starting at all.