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CANADA, UNITED STATES Document ID: IK1201498

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ENGINE

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6/3/2024

Current Language: English

Last Modified: 9/20/2024

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Greg Scheff

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Title : Adding a Shim to Certain Crankshaft Position Sensors (CKP) on A26B Engines
Applies To : Low mileage A26B engines

CHANGE LOG
Please refer to the change log text box below for recent changes to this article:
09/20/2024 - Initial Article Release

DESCRIPTION
Certain newly built vehicles equipped with the A26B engines were built with a 0.50mm thick shim under the crankshaft position sensor
(CKP). This was done due to an issue found after production with the TDC stamp on certain flywheels which could result in a DTC, or a
rough idle condition without a DTC. Primary application are vehicles equipped with the Allison automatic transmissions.
This article will call out those VINs that are equipped with the shim, and if and when the shim should be used as a field repair solution.

SYMPTOM(s)
Diagnostic Trouble Code(s) & Dashboard Indicator Light(s):
DTC/Light

Description

SPN 157 FMI 31

FRP: Condition Exists

SPN 637 FMI 8

Engine Timing Sensor: Abnormal
Frequency or Pulse Width or Period

Customer Observations or Concerns:
The engine may have a very rough idle, to the point it may shut down without any DTC setting at all. This affected engines primarily with
very low miles (less than 50K). It is possible as well to set the 637-8 CKP fault along with the rough idle condition. One other failure mode
seen, was the 157-31 FRP fault setting with a rough running or stumble complaint right before the trans would make a shift.

SPECIAL TOOL(s) / SOFTWARE
None

SERVICE PARTS INFORMATION
Kit Description

Part Number

Washer (Shim) 6.4 ID x 0.5 Thick

7108581C1

Quantity
Notes
Required
Only as
1
needed

DIAGNOSTIC STEP(s)
Step Action
DIAGNOSTIC: Has GUIDE diagnostics been completed on any active DTC's
without finding root cause?

Decision
Yes. Go to Step 2

NOTE: If diagnosing the 157-31, do NOT replace the HP Fuel Pump as it will not
resolve this issue.

No. Complete any applicable GUIDE
diagnostic procedures first, retest for the
condition.

#1

Step Action

Decision

DIAGNOSTIC: Inspect the TDC stamping on the Flywheel

Yes. Continue through published
diagnostics for any DTC's that are
Remove the inspection cover from the bottom of the flywheel housing, bar the present. If no resolution is found consider
engine over to TDC.
opening a tech service case file for further
assistance.
Visually inspect the TDC stamp and compare to Figure #1 below. If required,
measure the depth and the width to see if it is within specifications.
Maximum Width: 0.55mm
Maximum Depth: 0.275mm
#2
Is the TDC mark within specifications?

No. Continue to step 3

Figure #1: Flywheel TDC Stamp
Item 1: OK, mark is very light and narrow. Slightly more than a simple scribe marking
Item 2: NOT OK, mark is very deep and wide, when measured is out of specification listed in step 2

Step Action
DIAGNOSTIC: Verify if the engine was built with a timing sensor shim, or is a
shim already in place around the CKP sensor hold down bolt?

Decision
Yes. Replace the flywheel, verify the TDC
mark is within specifications before
installation.

Review the VIN list HERE to see if the engine was built with a timing sensor shim.
NOTE: remove the shim from under the
timing sensor hold down bolt once the
Was the engine built with a timing sensor shim, or does it have a shim already new flywheel is installed. Once back
installed?
together, retest for the condition.

#3

No. Proceed to step 4.

Step Action
DIAGNOSTIC: Install a 0.50mm shim under the crankshaft position sensor
hold down bolt.

Decision
Yes. Clear any DTC's and return the unit
to service.

Remove the crankshaft position sensor from the flywheel housing. Insure the sensor
tip is clean and undamaged. Install the 7108581C1 shim under the sensor and
around the hold down bolt (Figure #2 Item 1). This will lift the sensor from the
housing 0.50mm.
Install the shimmed sensor and torque the bolt to 13 +/- 1.3 Nm then retest for the
condition.
#4

Did installing the shim resolve the operational complaint?

Figure #2: Timing Sensor Shim Location
Item 1: Shim to be installed here, around the sensor hold down bolt

WARRANTY INFORMATION
Warranty Claim Coding:
Refer to the Warranty Coding Manual for Group and Noun Codes.

OTHER RESOURCES
Master Service Information Site

No. Consider opening a tech service case
file for further assistance.

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