Poor Splice Connection in 1.2L Engine Wiring Harness

A poor splice connection in the engine wiring harness on some 2020-2021 Trailblazer and Encore GX models equipped with the 1.2L engine (RPO LIH) may result in an illuminated Check Engine MIL and DTC P0521 (Engine Oil Pressure Sensor Performance).

If these conditions are present, run the engine, with the hood closed, to normal operating temperature and then use GDS 2 to view the engine oil pressure in PSI. Next, turn the engine off and place the ignition in Service Mode. Monitor the engine oil pressure for readings above 0.0 PSI. It may be necessary to close the hood and run the engine for an additional amount of time to duplicate the condition.

Once the engine oil pressure reading is above 0.0 PSI, open the hood and slightly bend the main engine wiring harness back-and-forth at the front of the engine (Fig. 5) while monitoring GDS 2 for a pressure change.


Fig. 5


TIP: If the engine oil pressure reading moves to 0.0 PSI while manipulating the harness, the reading may not change from 0.0 PSI without further movement of the harness.

A change in the engine oil pressure reading, either an increase or decrease in PSI, isolates the condition to this specific location on the engine wiring harness. A high resistance splice in the engine wiring harness above the EVAP purge pump may cause DTC P0521 to set.

Do not replace the oil pump or o​il pressure sensor without first diagnosing the potential splice concern, as this may result in a return repair visit.


Splice Location

The Service Information may show only one splice for low reference circuit 548 (J114). An additional three-wire splice has been added to the low reference circuit 548 (BK/GN).

The three-wire splice is located in the main branch of the engine wiring harness above the EVAP purge pump assembly. (Fig. 6)


Fig. 6


Open the engine wiring harness to access the three-wire splice and inspect each leg for broken wire strands. Repair any damaged wiring. (Fig. 7)

After repairs are completed, be sure to install an appropriately-sized heat shrink tube over the circuit and wrap the engine wiring harness with the appropriate PET underhood tape.


Fig. 7


– Thanks to Raymond Haglund


Updated December 3, 2021

TechLine Connect Software Update Adds New Direct Launch Programming Functionality
GDS2 Update Includes New MDI Tool Selection Window

One Comment

  1. Thank you for this repair! I did one coordinating with Raymond and I haven’t seen the vehicle back!

Leave a Reply

Your email address will not be published.