Symptoms To Detect Bad Glow Plug Relay On 7.3L Powerstroke

The 7.3 glow plug relay is at the passenger side engine valve cover behind the fuel filter housing, with brown and yellow wires attached. 

This control module is responsible for turning the glow plugs on and off. It is for starting the 7.0 powerstroke diesel engine in cold weather. Since this engine does not come with spark plugs, glow plugs play an important role here. 

However, many users have experienced 7.3 glow plug relay failure, but they could have prevented the problem if they were aware of the initial sign and symptoms to get a hint. 

Therefore, in this very article, let’s learn how to detect when your 7.3 glow plug relay needs immediate attention.

What Is The Sign Of A 7.3 Bad Glow Plug Relay?The most common and obvious signs of a 7.3 bad glow plug relay are when your engine suddenly stops or no proper voltage or connections.

7.3L Powerstroke Bad Glow Plug Relay Symptoms:

There are other significant symptoms by which you can easily identify when your 7.3 glow plug relay needs proper inspection and repairing or replacement. 

So, let’s learn more about those symptoms and how to detect a 7.3 bad glow plug relay –

1. No power

When some owners tried to start the 7.3 powerstroke engine, they face trouble with it starting. Lots of white smoke, and even with the block heater, it didn’t start below 30 F.

No power was getting on the switched terminal or large terminals. This could indicate a bad relay.

2. Faulty pcm

The pcm may not be grounding the relay. Check for power on the ground circuit directly at the pcm. If you have the power there, then the pcm is bad. 

3. Proper voltage

You should have voltage to the large lugs of the relay all the time, even when the key is off. It connects to the battery on the battery side terminal of the solenoid on the fender. 

So, if you don’t have any voltage, there may be a fusible like that may have blown between the solenoid and the relay.

4. Wrong connection

The gpr wire may be connected to the wrong side of the starter solenoid. So, you should check the connections for the proper result. 

When you want to figure out whether your relay is functioning okay or not, you can use a test light. 

  • Attach one test lead to each of the two large terminals. 
  • The test light should come on when you turn the key in the ignition.
  • Connect the battery to one of the two big terminals.
  • Now, when one test lead connects to the other big terminal and the second test connects to the ground, the light should be on when you turn on the ignition. 

The opposite big terminal should now be getting power if the relay is good. If not, then the relay is bad. 

These are the most commonly identified symptoms that indicate the 7.3 glow plug relay failure condition. So, if you also own one of the 7.3 Powerstroke engines on your vehicle, make sure to keep them in mind.

What to Do When You Detect a 7.3 bad glow plug relay?

The 7.3 glow plug relay is used in the glow plug control unit. Through the relay, you can turn the current switch on and off. A control unit often functions with glow plugs. 

On the contrary, a bad glow plug relay will affect the heating activity in starting a 7.3 Powerstroke engine in cold weather. Let’s us how you will react when you found out the 7.3 bad glow plug relay symptoms. 

Disconnect the wires from the small posts, take your jumper cables, connect positive 12V to one small post, negative to the other small post, and the relay should give an audible click. 

At this time, you’d measure 12V on the big output lug of the relay, up until the time you disconnect one of the jumper cables feeds.

Is Replacing A 6.7 Powerstroke CP4 Typically Expensive?

In order to decide if you need to replace it or not, you really need to check the relay with a digital meter to tell any difference. When you test the post, there should be less than 0.3 of a volt difference between them. 

You need to follow some steps to replace the relay –

  • Remove the wiring harness
  • Mark the position of the four wires attaching to the two large and two small terminals.
  • Remove the wires
  • Unbolt the relay from the valve cover
  • Bolt the replacement unit into place
  • re-attach the wires to the terminals 

And when you have to replace it, the cost will be around $500-$750, including parts and labor.

Final Thoughts

These 7.3 glow plug relays help the higher current circulation in the circuit. Using a glow plug relayed across the circuit will reduce higher current or maintain existing functionality. The glow plug relays are appropriate for older glow plug systems such as 7.3 Powerstroke.

Therefore, any slight issue with the relay is real bad news, but prevention can help you keep your relay healthy, and those above discussed symptoms will help keep a close eye on your relay to prevent any severe issue.

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