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Dan, ASE Certified Technician
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2003 Chevy Tahoe Z71. Service 4WD message appears randomly.

Customer Question

2003 Chevy Tahoe Z71. Service 4WD message appears randomly. When starting engine, 4WD selection buttons are lighted differently each time. Sometimes in Nuetral, 2hi, 4hi & 4lo. Cannot select any option, stays on what it is in when started. Got code P1875.
Submitted: 5 years ago.
Category: Chevy
Expert:  Vladgmru replied 5 years ago.
Hi Scotie!
My name is Vladimir.
GM has a TSB related to this issue.
You can either replace or repair 4WD selection switch.
If you are familiar with a soldering iron, just remove the switch, disassemble it and resolder all the suspicious points in the circuit board.
Have a good time!
Customer: replied 5 years ago.
Do you have the TSB for this for my reference.
Expert:  Dan replied 5 years ago.

hello ,

 

There is a bulletion for this to replace the encoder sensor. Easy to do. No soldering required. It also has a updated calibration for the module. You could try it your self but the dealer would have to program. here is a copy of the bulletion.

 

#03-04-21-001D: 4WD Switch Indicator Lights Flashing, 4WD Inoperative, DTCs C0327, P0500, P0836, P1875 Set (Replace Encoder Motor Sensor, Reprogram TCCM, Inspect Front Drive Axle Engagement Sleeve for Damage/Repair) - (Dec 4, 2003)

Subject:4WD Switch Indicator Lights Flashing, 4WD Inoperative, DTCs C0327, P0500, P0836, P1875 Set (Replace Encoder Motor Sensor, Reprogram TCCM, Inspect Front Drive Axle Engagement Sleeve for Damage/Repair if Necessary)

Models:2003 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2003 GMC Sierra, Yukon, Yukon XL
with 4WD and Electric Shift or Active Transfer Case (RPO NP1 or NP8)

 


Condition

Some customers may comment that the Service 4WD light is on, the 4WD system is inoperative, the 4WD switch indicator lights are blinking or that a grinding noise is heard from the front axle.

Service Diagnosis

Technicians may find DTC C0327 in the Transfer Case Control Module (TCCM) and/or DTC P0836 in the Transmission Control Module (TCM) and/or DTC P0500 and P1875 in the Powertrain Control Module (PCM).

It is possible that the module may be in a mode that will not allow any shifts or updates for the software or calibrations. If this occurs, the TREC fuse (in the engine compartment) must be pulled and reinstalled after 30 seconds. This should allow further operation and service of the system. If a C0550 code is found, this is an unrelated concern and SI diagnostics should be followed for this concern.

Correction

Important: For ease of reassembly, shift the transfer case assembly to 2HI for the NV263 (NP1), or Neutral for the NV246 (NP8) prior to removing any components. For information on placing the NV246 (NP8) transfer case in NEUTRAL, see the procedure at the end of this bulletin.

  1. Remove the transfer case and front axle/engine skid plates (if equipped).
  2. Disconnect and position the front propeller shaft aside.
    Object Number: 857301  Size: SH

  3. Disconnect the transfer case encoder motor wiring harness.
  4. Remove the three (3) bolts that retain the encoder motor to the transfer case.
  5. Separate the encoder motor assembly from the transfer case and place it on a work bench.
    Object Number:(NNN) NNN-NNNN Size: MF

    Important: DO NOT REMOVE THE SCREWS INDICATED WITH THE (1) IN THE ABOVE ILLUSTRATION.

  6. Remove the four screws on the outer perimeter of the encoder motor housing.

    Important: For proper timing and ease of reassembly, hold the gear in place as your remove the cover from the encoder motor assembly with your thumb or finger.

  7. Carefully remove the cover from the encoder motor assembly. The cover has a seal on the bottom side. Place the cover in a position to protect this seal from damage and/or contamination.
    Object Number:(NNN) NNN-NNNN Size: MH

    Important: Observe the location of the punch mark on the large gear in relation to the timing mark on the housing if the transfer case was placed in the 2HI for the NV263 (NP1), or Neutral for the NV246 (NP8). The timing marks should be within one tooth of proper alignment. If not, you must note the timing mark positions for reassembly.

  8. Locate the two shims; one on the small gear and another on the larger gear. Set them aside on a clean surface for reuse.

    Important: After removing the large gear from the housing, a dark gray phenolic spacer should remain in the casting where the bottom of the large gear resides. Locate this spacer and save for reuse.

  9. Carefully lift the large gear from the housing. The sensor and wiring harness will come with the gear.
  10. Disconnect the wiring from the sensor.
  11. Separate the sensor from the large gear.
    Object Number:(NNN) NNN-NNNN Size: SH

  12. Ensure the phenolic spacer is in position in the housing.
    Object Number:(NNN) NNN-NNNN Size: SH

    Important: The sensor has two (2) keyed areas which must be properly positioned when reassembled. The bottom of the sensor has a positioning pin that must be positioned in the cavity in the housing. The sensor key must be properly positioned over the key way in the large gear. Follow the step by step instructions below for ease of assembly.

  13. Carefully position the new encoder sensor to the large gear aligning the key way slots. Just begin the insertion of the keyway over the key. Press the sensor onto the large gear using a ¾ inch deep well socket. This will ensure proper installation of the sensor.

    Notice: Not using the socket to press the sensor on may result in damage to the sensor.

  14. Connect the wiring harness to the sensor. The wiring harness connector wording (TOP) must face up or toward large gear.
  15. Position the sensor and gear into the housing with the positioning pin seated in the housing. Align timing marks on the large gear and housing previously mentioned.
  16. Reinstall the shims on the small and large gears.
  17. Ensure that the wiring harness is properly seated in the housing.
  18. Replace the encoder motor cover seal.
  19. Reinstall the cover with the four (4) new screws.

    Tighten

    Tighten the two (2) long screws to 3.38 N·m (30 lb in).
    Tighten the two (2) short screws to 2.25 N·m (20 lb in).

  20. Place the encoder to transfer case gasket into position on the dowel pins in the transfer case.
    Object Number: 857328  Size: SH

  21. Reinstall the encoder motor assembly to the transfer case.

    Tighten
    Tighten the bolts in the sequence shown to 20 N·m (15 lb ft).

  22. Reconnect the encoder motor wiring harness connector.
  23. Reinstall the front propeller shaft.
  24. Reinstall the transfer case skid plate, if equipped.
  25. Disconnect the wiring from the front axle actuator motor and the axle housing.
  26. Remove the right stabilizer shaft link assembly.
  27. Remove the six (6) right front wheel axle shaft companion flange bolts. Reposition the right front axle shaft away from the companion flange.
  28. Remove the five (5) inner axle shaft housing bolts from the differential carrier case.
  29. Remove the two (2) axle shaft housing nuts from the bracket.

    Important: When the right front axle tube is removed from the vehicle, several components may fall out. Position a receptacle such as the engine oil drain with screen under the front differential carrier to catch these components.

  30. Position an oil drain pan under the front axle, as about ½ cup of differential fluid may drain from the differential as the right front axle tube and shaft assembly is removed from the vehicle.
  31. Remove the right front axle tube and shaft assembly from the vehicle.
  32. Inspect the engagement sleeve for damage to the internal teeth. If damage is found, replace the sleeve. This sleeve is powdered metal and will fracture if dropped.
  33. Clean the end of the axle/tube assembly and the differential carrier flange of the original sealer.
  34. Clean any metal shavings out of the axle housing if there are any, including flushing the fluid if needed.
  35. Position the axle/tube assembly with the companion flange resting on the bench.

    Important: The bevel on the outer circumference of the engagement sleeve must be positioned into the axle shaft tube assembly.

  36. Reassemble the right front drive axle components ensuring that the spring is properly positioned over the end of the fork assembly , and that they are positioned to the engagement sleeve and the pilot in the axle shaft tube.
  37. Apply sealant, GM P/N(NNN) NNN-NNNN(Canadian P/N 10953466), or equivalent, to the axle housing to differential carrier sealing surface.
  38. Position the axle/tube assembly to the differential carrier and the mounting bolts.

    Tighten

    Tighten the axle/shaft assembly to frame bolts to 100 N·m (75 lb ft).
    Tighten the axle/shaft assembly to differential carrier bolts to 40 N·m (30 lb ft.).

  39. Reposition the right front axle shaft to the companion flange and install the (6) bolts.

    Tighten
    Tighten the bolts to 79 N·m (58 lb ft).

  40. Install the right stabilizer shaft link assembly.

    Tighten
    Tighten the stabilizer shaft nut to 10 N·m (89 lb in).

  41. Route and reconnect the wiring harness.
  42. Verify the fluid level in the front differential. If fluid is required, fill with SAE 80W-90 Axle Lubricant, GM P/N(NNN) NNN-NNNN(Canadian P/N 10950849), or equivalent.
  43. Reinstall the skid plates (if previously removed).
  44. Shift the NV246 (NP8) transfer case to the 2HI position. See procedure below. (The NV263 (NP1) should already be in 2HI)
  45. REPROGRAM THE TCCM IN THE 2HI POSITION for the NV263 (NP1) and NV246 (NP8).

Shifting NV246 (NP8) Transfer Case into Neutral

  1. Set the parking brake.
  2. Turn the ignition to the RUN position.
  3. Place the vehicle transmission in Neutral.
  4. Shift the transfer case to 2HI.
  5. Simultaneously press and hold the 2HI and 4LO buttons for ten (10) seconds. The RED Neutral light will come on when the transfer case shift to Neutral is complete.
  6. Shift the transmission to Reverse (R) for one second, then shift the transmission to DRIVE (D) for one second.
  7. Turn the ignition OFF. Place the shift lever in Park (P).

Shifting NV246 (NP8) Transfer Case into 2HI

  1. Set the parking brake.
  2. Turn the Ignition switch to the RUN position.
  3. Place your foot on the brake pedal and apply the brakes.
  4. Move the transmission shift lever to NEUTRAL (N).
  5. Press the button for 2HI. The transfer case Neutral light will go out and the transfer case will be in 2HI range.
  6. Turn the ignition to the LOCK position.

Parts Information

Part Number

Description

Qty

88962315

Sensor, Transfer Case Encoder, (NV246, NP8)

1

88962313

Sensor, Transfer Case Encoder, (NVG263, NP1)

1

12384990

Seal, Transfer Case Encoder Motor Cover

1

12384988

Screw, Transfer Case Encoder Motor Cover

2

12384989

Screw, Transfer Case Encoder Motor Cover

2

26064275

Clamp, Prop Shaft

1

12479006

Sleeve, Front Drive Axle Engagement (9.25" Axle)

1

(If required)

26033974

Sleeve, Front Drive Axle Engagement (8.25" Axle)

1

(If required)

Parts are expected to be available from GMSPO on December 18, 2003.

Expert:  Dan replied 5 years ago.
Before you replace any parts, Check the codes in the transfer case module. More than likely it will be a C0327. Thanks
Expert:  Vladgmru replied 5 years ago.
I am sorry Scotie but I am at home right now and don't have access to service manual.
I will try to find it on friday when I return to work.
Customer: replied 5 years ago.

Your first response was to replace the selection switch, and the TSB is replacing the encoder sensor. Are we talking about the same item. The TSB looks quite in depth. Will replacing the selection switch require any reprogramming? I'm a little confused? I have not checked the TCM for codes, but will.

 

I am at work, but have a service manual at home and will check also.

Expert:  Dan replied 5 years ago.

OK, The bulletin explaines how to replace the sensor inside of the encoder motor. Thats why its so long.

 

Another tech/Expert here (Vladgmru) told you about a selection switch. I don't agree with that.

 

Yes, It would need to be reprogramed. There is an updated calibration for the Transfercase Control module (TCCM) to work with this new sensor to prevent this problem and another problem from the module not comming on when you start the vehicle.

 

I'm sorry for the confusion, I normally don't respond to other experts information unless I see a problem with what they are saying.

 

The Transfer case module has its own set of codes that need to be checked. Most scan readers won't pull up those codes. You got a P1875 from the engine module.

 

Hope this clears up some things. Let me know if I need to explan something else

 

ThankYou for using JUST ANSWER

Customer: replied 5 years ago.

I'm sure you saw my initail question, but my main gripe is the 4WD selection switch is in a different posistion every time I crank up, and cannot be moved into another selection? Just to clarify, you believe the problem is in the encoder sensor, not the selection switch?

 

Is this selection switch a common failure?

 

 

Expert:  Vladgmru replied 5 years ago.
I am sorry Scotie, whom are you asking me or Dan?
Expert:  Dan replied 5 years ago.

The switch light up the positon the encoder is in. When you push a button on the switch, it sends a signal to the transfer case module. the module ignores if due to the code set in the module. The encoder sensor is off and sending a wrong signal to the module, which in make the switch light up different position.

 

You need to get codes checked in the transfer case module to confirm .

 

Thanks

Customer: replied 5 years ago.

That makes sense. When I select a different drive, it blinks for about 20 secs or so, then returns back to the initial it was in.

 

My code reader does not read TCM, so I'll have to check with a dealer to read.

 

Is this TSB a high $$ fix throught the dealer?

 

I'm also a first time user to Just Answer, so will accepting this answer end all conversation, or can I revisit after I find out TCM codes? I want to pay, just don't want to cut my question off to soon.

Expert:  Dan replied 5 years ago.

I don't see the paperwork end of these repair, I think they run $300-500. Just a guess.

 

You can leave it open I guess, i'm not totally sure how it works on your end. You can always request me ar ping me. Thanks for Using Just Answer

Dan, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2270
Experience: 20 Year Factory Trained Current GM Technician
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