MIL illuminated with DTC P0521 – 2020-2021 Buick Encore GX & Chevrolet Trailblazer

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Bulletin No.: PIP5826B Published date: 12/22/2021
Preliminary Information
PIP5826B MIL illuminated with DTC P0521
Models

Brand:

Buick Chevrolet

Model:

Encore GX Trailblazer

Model Years:

2020 – 2021
2020 – 2021

VIN:
from to
All All
All All

Engine:

1.2L (LIH)
1.2L (LIH)

All All

Transmissions:

Involved Region or Country

Condition Cause

North America
Some customers may comment that the MIL light is illuminated. A P0521 may be stored Current or in
history.
This may be caused by high resistance in the engine wiring harness.
Correction:
Run the engine with the hood closed until normal operating temperature is achieved.
Connect GDS2 to the vehicle and enter Module Diagnostics / Engine Control Module / Data Display /
Engine Mechanical Data.
Lock GDS2 Parameter: Engine Oil Pressure in PSI.
Note: GDS2 Parameter: Engine Oil Pressure Sensor or GDS2 Parameter: Absolute Engine Oil Pressure
are not usable for this testing.
Start the engine.
Validate proper engine oil pressure.
At idling speed, engine oil pressure should be 160 – 200 kPa (23.21 – 29.01 psi) and the oil
temperature must be between 80°C (176°F) and 100°C (212°F).
At 4000 rpm, engine oil pressure should be 340 – 380 kPa (49.31 – 55.11 psi) and the oil
temperature must be between 80°C (176°F) and 100°C (212°F).
If the engine oil pressure is within specification, use the pictures shown below to locate the
engine wiring harness part number tag.
It is located on the harness branch for X50A Fuse Block – Underhood as shown below.

Branch for X50A Fuse Block – Underhood.

Engine wiring harness part number tag.

If the part number is one of the following (42737310, 42737311, 42749493, 42749494), inspect the
three ECM connectors for proper locking lever and CPA lock positions. (refer to picture below).

Use the appropriate Global Service Information documents to locate and inspect the following
circuits for bent pins or poor terminal tension.
Circuit 460 5V1 Reference Bus at ECM. Circuit 580 Low Reference Bus at ECM.
Inspect the 4 clips circled below for broken Tie Straps and proper retention of the main engine
wiring harness.

If the engine oil pressure is within specification, turn the engine off and immediately press and
hold the Start button to enter Service Mode.
While in service mode, monitor the Engine Oil Pressure parameter for readings above 0.0 PSI. (You
may have to close the hood and run the engine for additional time to duplicate)
Once duplicated, open the hood and bend the harness back and forth at the circled location shown
below while monitoring for the engine oil pressure to change.

Note: If the engine oil pressure reading moves to 0.0 PSI while manipulating the harness, the
reading may not change from 0.0 PSI with additional manipulation.
A change in the engine oil pressure reading either up or down in PSI, isolates the issue to the
Special three wire Splice in this location of the main engine wiring harness.
Note: Not all of the listed harnesses will have the Special three wire splice.
Open the engine wiring harness in the location circled above to access the three wire special
splice for Low Reference circuit 548 BK/GN.
Remove the Heat Shrink and splice clip to expose all three legs of the special splice.

Inspect each leg for broken wire strands and correct any issues.
Slide the appropriate size heat shrink tube on one branch of the circuit. Install a new splice
clip, solder the three legs, and seal with the heat shrink.
Close the main engine wiring harness using the appropriate PET under hood tape.

NOTE: This PI will be updated or changed to a bulletin as more information becomes available
Warranty Information
For vehicles repaired under the Powertrain coverage, use the following labor operation. Reference
the Applicable Warranties section of Investigate Vehicle History (IVH) for coverage information.
Labor Operation Description
Labor Time 5486268* Splice Repair
1.0 Hr.
*This is a unique Labor Operation for Bulletin use only.
Version History
Version 3
11/08/2021 – Created on.
11/09/2021 – To update GDS2 Verbiage

Modified 12/22/21 – To add additional testing procedures.

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