The OBD2 port on a 2003 Yukon Denali is essential for diagnosing engine problems. This guide will troubleshoot a non-working OBD2 port and a cigarette lighter only outputting 6 VDC, assuming fuses visually appear okay.
Check Fuse 13 in the Underhood Fuse Box
The first step is to replace Fuse 13, a 20 Amp fuse, in the underhood fuse box. Even if the fuse looks intact, it might be blown or defective. Dirty or oxidized terminals on the fuse can also cause issues. After replacing Fuse 13, check if the OBD2 port is active and if the cigarette lighter now has a 12 VDC reading.
Understanding the Circuit
The OBD2 port and the cigarette lighter share a simple circuit connected to Fuse 13. Power flows from the load side of Fuse 13 directly to pin 16 of the OBD2 port and the center terminal (Pin A) of the cigarette lighter. The wiring diagram illustrates this connection.
Testing for Voltage
If the cigarette lighter still lacks 12 VDC, use a multimeter (digital preferred) to check for voltage at Fuse 13. With the multimeter in DC volts mode and the black lead grounded, touch the positive probe to each exposed pin of Fuse 13. You should measure 12 VDC on both sides.
Testing for Continuity
If 12 VDC is not present on both sides of Fuse 13, switch the multimeter to ohms mode. Connect one lead to the 0 voltage side (load side) of Fuse 13’s contacts and the other lead to pin 16 of the OBD2 port. A reading of zero ohms indicates a good connection. A higher reading suggests a wiring issue between the OBD2 port and the fuse box, requiring further tracing.
Next Steps
If Fuse 13 was the problem, you should now be able to connect a code reader or scanner to the OBD2 port. Retrieve any stored codes and report them back for further assistance in diagnosing the root cause of the initial problem.
