Service 4WD Message C0398 – 2014-2016 Cadillac Chevrolet & GMC

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Subject:	Service 4wd Message C0398
Models:	2014-2016 Chevrolet Silverado
	2015-2016 Chevrolet Suburban Tahoe
	2014-2016 GMC Sierra
	2015-2016 GMC Yukon
	2015-2016 Cadillac Escalade
	2015-2016 GMC Canyon
	2016 Chevrolet Colorado

Condition/Concern

Some customers may comment on a “Service 4wd” message displayed in the DIC. Upon investigation dealer may notice a C0398 in the tccm along with a U0403 and U0102 in various other modules.

Recommendation/Instructions

When DTCs set in the TCCM it also causes U0403 to set in various modules along with the U0102. Correct the DTCs in the TCCM first.

When diagnosing a C0398 if there are any other diagnostic trouble codes related to transfer case actuator position sensor (IPS) or rotational position sensor (RPS) diagnose and repair those first. Those diagnostic trouble codes may be intermittent and move to history but once a C0398 is set it can only be cleared with a scan tool and will never move to history on its own or clear by key cycles, At this time you need to clear the DTC 2 times to clear the code from the TCCM.

Since C0398 sets when IPS and RPS differ by more than a predetermined amount, terminal or circuit issues can lead to a position sensor reading that is incorrect yet not be out of range far enough to set a code against the related sensor (IPS or RPS). That is why it is beneficial to record any codes set with C0398. If the condition cannot be reproduced and there was a code C0396 also stored but will not reset then there is a high probability of having an issue with the IPS related circuits.

FOR 2014 Model year Silverado and Sierra or 2015 Model year Pick up, utilities and Canyon equipped with NQH, NP0 or NQ6 vehicles setting a C0398 (no other codes C0392/C0396/C0326) ensure that Service Update 15304 has been completed, indicating the vehicle has the latest transfer case control module software/calibration.

For vehicles that already have previously completed 15304 check circuits related to IPS/RPS for chaffed wires or poor terminal tension. Note there are 2 different terminals used in the transfer case control module connector which also have a different tension. However the terminal test tool should be retained in either terminal.

For vehicles that do not have 15304 completed, perform 15304 and after programming perform the set up procedure in Tis 2 Web then check circuits related to IPS/RPS for chaffed wires or poor terminal tension. Note there are 2 different terminals used in the transfer case control module connector which also have a different tension. However the terminal test tool should be retained in either terminal.

FOR 2014 Model year Silverado and Sierra or 2015 Model year Pick up, utilities and Canyon equipped with NQH, NP0 or NQ6 setting a C0398 with codes C0392 or C0396 perform published diagnostics for the other codes and repair as needed. If diagnostics do not lead to a repair then check circuits related to IPS/RPS for chaffed wires or poor terminal tension. If 15304 has not been performed, diagnose and repair the C0392/C0396 first then perform 15304 before returning the vehicle to the customer. Note there are 2 different terminals used in the transfer case control module connector which also have a different tension. However the terminal test tool should be retained in either terminal.

Note: The latest version of software/calibration contained in 15304 and start of production 2016 model year vehicles eliminated the possibility of the transfer case control module setting C0398 on cold start when the vehicle was shut off in auto 4 wheel drive due to a mechanical anomaly in the actuator motor. Previous to this software release actuator motors part number 23355888 may have been installed, however in 2015, as an interim fix, the actuator motor was changed in production to a production equivalent of 23355888. The latest version of software/calibration has provisions to identify this anomaly and it is no longer necessary to replace actuator motors. If the vehicle sets C0398 on start up in auto 4 wheel drive then again check circuits related to IPS/RPS for chaffed wires or poor terminal tension.

FOR 2015 Model year Pick up, utilities and Canyon equipped with NQH, NP0 or NQ6 Built after 05/26/2015 and all 2016 Model year Pick up, utilities Colorado and Canyon equipped with NQH, NP0 or NQ6 setting a C0398 with no other diagnostic trouble codes such as 0392/0396, verify the latest transfer case control module software as compared to what is currently in the TCCM and what is available through Tis2Web. It is very important to follow the strategy below to accurately diagnose and repair these vehicles.

1: Contact the customer and determine if the vehicle was driven an extended period (longer than 1.5 hours) in Auto 4 wheel drive when the message came on or just prior to the message coming on.

If the customer indicates that the message came on while on an extended drive cycle in auto 4 wheel drive or was on at start up following an extended drive cycle in auto 4 wheel drive look at the tag on the actuator motor. If the part number in the lower right corner is M0033357 (1) then replace the actuator motor. If the part number is M0040350 (2) then look at the number in the upper right corner of the tag (3), If the first 6 digits (left to right) of the number in the upper right hand corner are higher than 150523 then replace the actuator motor. (These are NOT G.M. part numbers refer to the parts catalog for current replacement parts)

For actuator motors with any other numbers in the lower right corner (1 or 2) or vehicles that have not been driven for extended periods (less than 1.5 hours) in auto 4 wheel drive look at transfer case control module data in GDS2. Select the following parameters to be locked at the top of the screen. Range Actuator Position Sensor, Transfer Case Range Position Sensor, Variation Between Transfer Case Range Position Sensor and Range Actuator Position Sensor, Variation Allowed Between Transfer Case Range Position Sensor and Range Actuator Position Sensor, Transfer Case Range Position Sensor, and Engine Run Time. The table below contains the parameter names from the Transfer Case Control Module in GDS and is NOT an exact representation of the GDS screen or format.

Monitor Range Actuator Position Sensor (IPS), Transfer Case Range Position Sensor (RPS), Variation Between Transfer Case Range Position Sensor and Range Actuator Position Sensor and wiggle the harness while watching the data. If data indicates a sensor or variation changing over 1.5* perform circuit testing related to the suspect sensor. It is normal to see 0-.3 degrees variation while driving in auto 4 wheel drive

Warranty Information

For vehicles repaired under warranty use:

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