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2008 F350 6.4L Engine Shows U0073 and U0100 OBD2 Codes When External Electronics Are Connected

Model: 2008 F350 Fault Code: U0073 Posted: 2019-01-14 17:07

I own a 2008 Ford F350 with a 6.4L V8 engine. I've noticed that when a tuning device is connected via the OBD-II port, my truck intermittently displays U0073 and U0100 diagnostic trouble codes. These codes disappear completely when the tuner is unplugged. The same sporadic appearance of these codes occurs when an OBD-II reader or monitor is plugged in—disappearing again once disconnected. I've tested this with both a new tuner and a standalone OBD-II scanner, and the behavior remains consistent. Notably, if no external device is connected to the OBD-II port, the codes do not appear at all. This pattern suggests an interference issue rather than a hardware failure in the engine control module or fuel system. I'm wondering whether this could be due to electromagnetic interference from aftermarket electronics or a faulty OBD-II port.

Related fault codes
U0073U0100
Comments (3)
Anonymous 2019-01-15 14:22

Most likely culprit: a bad tuner. Any added electronic device should be the first suspect, especially those that inject signals into the vehicle's ECU via the OBD-II interface.

Anonymous 2019-01-17 14:22

I've tested this with both a new tuner and a basic OBD-II reader—same result. The codes only appear when any external device is connected to the OBD-II port, and vanish completely when unplugged. This strongly indicates that the issue stems from signal interference rather than a vehicle-specific fault.

Anonymous 2019-01-17 16:44

The truck ran for several years without issues with a tuner installed. The first appearance of U0073 and U0100 codes occurred approximately one month after the truck was serviced at the dealership for a new front engine cover under warranty. This timing suggests a possible connection between the service event and the onset of the codes, though no direct link has been confirmed.