Bulletin No.: PIT5457C
Published date: 06/12/2018

Preliminary Information
PIT5457C Service ABS / TCS / Power Steering and/or Suspension
Message DTC U0077 U0121 U0126 U0131 U0139 U0151 U0401
U0415 U0428 (Circuit 5986)
Product Investigation Review Required
Models
Brand:

Model:

Model Years:

VIN:
from

to

Engine:

Transmissions:

Cadillac

Escalade

2015 - 2018

All

All

All

All

Chevrolet

Silverado 1500

2014

All

All

All

All

Chevrolet

Silverado

2015 - 2018

All

All

All

All

Chevrolet

Suburban

2015 - 2018

All

All

All

All

Chevrolet

Tahoe

2015 - 2018

All

All

All

All

GMC

Sierra 1500

2014

All

All

All

All

GMC

Sierra

2015 - 2018

All

All

All

All

GMC

Yukon

2015 - 2018

All

All

All

All

Supersession Statement
This PI was superseded to add the 2018 Models and update the Condition and Recommendation. Please discard
PIT5457B.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition / Concern
Some owners may comment on any of the following issues:
- Service ABS and/or Traction control lights/message on.
- Service Power Steering System, if equipped with electric power steering.
- Service Suspension System, if equipped with RPO Z95.
- Backup reverse camera inoperative
- Backup camera grid or guidance lines missing/inoperative
- Vehicle Settings icon grayed out
- Loss of communication with EBCM, SDGM, SDM, SWPS, PSCM, PTO, HMI, and/or SCM (if
equipped).
- DTC's: B127B, U0077, U0117, U0121, U0126, U0131, U0139, U0151, U0401, U0415, U0428,
U18A3, and/or U2179
These concerns could be caused by high resistance/open/short in the Communication Enable
circuit 5986. The BCM activates this circuit when the ignition key is in ACC, ON, and START
positions (There will be voltage present in the OFF position only for a short time until the
BCM goes to sleep). The communication enable circuit wakes up the module for serial data
bus communication. Circuit 5986 will have approximately 12 volts and should light a test
light, but is not designed to handle heavier electrical loads like a headlight bulb.

Recommendations / Instructions
Monitor the voltage on the communication enable circuit 5986 at any of the modules
affected, example EBCM, SDGM, PSCM, SWPS, SDM, HMI, PTO, and/or SCM. If low voltage or

no voltage is present when the concern occurs, inspect for open/high resistance/shorts on
circuit 5986. Repair any opens/high resistance/shorts in the circuit.
Tips:
- Circuit 5986 is a low amperage signal circuit and it may not be able to power certain test
lights or bulbs. The use of a voltmeter and small bulb, example 194 bulb, is required to load
test the circuit. With a battery charger/maintainer connected to the vehicle, attach one side
of a 194 bulb to circuit 5986 (at the suspect module) and the other side to a good ground
(battery negative). Next, wake up the BCM (by turning the headlights on, turning
the ignition on, ect.) and make sure the bulb lights. If the bulb does NOT light, inspect for
high resistance/open/shorts in circuit 5986. If the bulb lights, use a voltmeter and measure
the voltage across the 194 bulb, to make sure there is at least 11 volts, if not inspect
for high resistance/open/shorts in circuit 5986. A 194 bulb draws approximately 250 ma.
Attaching too much of a load to circuit 5986 will pull the voltage down below 11 volts and
lead to misdiagnosis.
- The BCM monitors circuit 5986 for an excessive amperage draw and will shut down the
output on circuit 5986 if it draws more than 0.88 amps (example short to ground).
- The BCM 1 and BCM 2 fuses are what the BCM uses to feed power to circuit 5986.
Below are three known areas where circuit 5986 has been found to be open/shorted/high
resistance:
1. On short wheel base utilities (Escalade, Tahoe and Yukon), the chassis harness
cut/pinched/shorted between the body and spare tire crossmember, see latest version of
PIT5556 for more details.
2. Under the driver's sill plate, shown below.

3. Splice J365 located under the passenger front sill plate, shown below.

Warranty Information
Please refer to latest version of bulletin 10-00-89-005 for warranty information on
wire/connector repairs.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is
resolved without completing every step, the remaining steps do not need to be performed.

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