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2000 Ford Excursion 7.3L P0683 Error Code: Unable to Communicate with Glow Plug Module (GPM) - Relay vs Module Issue

Model: 2000 Ford Excursion Fault Code: P0683 Posted: 2016-01-27 16:09

I own a 2000 Ford Excursion with the 7.3L diesel engine and am currently experiencing the P0683 diagnostic trouble code, which indicates 'Unable to communicate with Glow Plug Module (GPM)'. Important clarification: My vehicle is equipped with a Glow Plug Relay (GPR), not a Glow Plug Module (GPM). The glow plugs do not heat up at all — they only activate when the engine is cold. This issue becomes noticeable in temperatures below 40°F, where starting the truck becomes difficult. The engine starts fine when ambient temperature is above 40°F, but struggles to start in the 30s. I've ruled out a simple wiring fault by testing the old relay independently on a battery — it clicked when grounded properly, indicating it's functional. My current theory: The Powertrain Control Module (PCM) is not sending a proper ground signal to the glow plug relay, which prevents the system from activating the glow plugs. I have a scan tool and a digital multimeter, but given my vehicle has a 6-inch lift and 35-inch tires, I'm planning to take it to a mechanic with more experience in diesel systems. I've also considered whether an engine oil temperature sensor might be faulty — if the PCM incorrectly reads oil temperature as 'hot', it may disable glow plug operation. This is a possibility worth exploring. Could the P0683 code be triggered by a misidentification of the GPM when I actually have a relay? Does this code apply to both modules and relays, or only specific configurations? I'm seeking community input on possible root causes — especially whether the issue lies in wiring, sensor readings, or hardware like a performance chip installed in the PCM.

Related fault codes
P0683
Comments (12)
Anonymous 2016-01-27 16:40

Trouble Code Conditions: When the engine is started, system voltage ranges from 11–15.0V, and the Powertrain Control Module (PCM) detects an unexpected voltage condition on the glow plug data line circuit. Possible Causes: • Glow plug diagnostic circuit is open or shorted to ground • Glow plug diagnostic circuit is shorted to system power (B+) • Glow Plug Control Module (GPM) is damaged or has failed • PCM has failed • Technical Service Bulletin (TSB) 99-25-10 provides a repair procedure for this code — however, it is only applicable in California and applies to vehicles with a glow plug module. Note: You have a relay, not a glow plug module — confirm this. This information may help clarify the issue. Reference: https://www.youtube.com/watch?v=3zEKy2koCfE

Anonymous 2016-01-27 17:09

Yes, I have a Glow Plug Relay (GPR), not a Glow Plug Module (GPM).

Anonymous 2016-01-27 17:11

Additional note: The truck starts without issues when temperatures are above 40°F. Starting becomes difficult in the 30s, especially during colder mornings.

Anonymous 2016-01-27 17:31

Did the video explanation help clarify the issue?

Anonymous 2016-01-28 06:32

Not really — I recently replaced the relay with a new one. When I tested the old relay separately on a battery, it clicked when grounded (as expected), indicating it was functional. My best current theory is that the PCM isn't sending a proper ground signal to the glow plug relay — this may be the root cause.

Anonymous 2016-01-28 08:36

Are you comfortable using a digital volt-ohm meter (DVOM) and referring to wiring diagrams? Do you have access to a professional-grade scan tool?

Anonymous 2016-01-28 09:56

Yes, I do have both a scanner and a voltmeter. However, I'm not a beginner anymore — this vehicle has a 6-inch lift and 35-inch tires, making it difficult to access for DIY work. I’m taking it to a trusted mechanic who is younger and more experienced in working on diesel trucks. Based on my research, the PCM may be failing to provide a ground signal to the glow plug relay. I’ll update once the mechanic completes diagnostics — and will share findings with the community. One theory I’ve seen online suggests that a faulty engine oil temperature sensor could falsely report hot oil temperatures, causing the PCM to disable glow plug operation.

Anonymous 2016-01-28 10:00

Could the PCM be detecting a Glow Plug Module (GPM) when in reality I only have a Glow Plug Relay (GPR)? Does the P0683 code cover both configurations, or is it specific to vehicles with GPMs?

Anonymous 2016-01-28 13:50

The P0683 code — confirmed via your scanner. Are there any other diagnostic codes present? A professional-grade scanner may provide more detailed data. This vehicle has federal emissions compliance — verify this by checking the radiator support decal to confirm emission package. Yes, the PCM uses input from multiple sensors (like oil temperature) to determine when glow plugs should activate. That’s why I asked about other codes. An open wire between the relay and the PCM could be a contributing factor. A DVOM and wiring diagram will be essential for diagnosis. Professional scanners often support bi-directional communication, allowing technicians to command glow plug activation — this can help test circuit functionality more effectively.

Anonymous 2016-01-28 16:25

I believe I’ve found the root cause: The PCM has a TS Performance Chip installed. After removing it and erasing all codes, turning the key on resulted in a noticeable drop in voltage on the dash gauge — the engine started smoothly on first crank with no P0683 code present. I’ve sent the chip back to the manufacturer along with the original PCM software code for analysis. They responded last Wednesday. I’ll update once I receive their findings — this may be helpful for others considering performance chips in diesel trucks.

Anonymous 2016-01-28 16:36

It appears you are not the original owner of the vehicle. A more experienced technician would likely have already diagnosed and addressed this issue. Always recommend staying with stock components — aftermarket modifications like performance chips can introduce unexpected issues. I wonder why Ford’s engineering team doesn’t use standard, factory-approved chip programs in their vehicles. Glad you found a solution!

Anonymous 2016-02-07 10:13

The chip has been returned to the manufacturer along with the PCM software code. They’ve responded and will provide feedback soon. I’ll update once I receive results — this may be useful for others researching performance chips and their impact on diagnostic codes.