Chevrolet Silverado: Transfer case encoder motor failure with 'Service 4WD' light (NP246 Autotrac)
Transfer case encoder motor failure with 'Service 4WD' light (NP246 Autotrac) is a common transmission fault on the Chevrolet Silverado on the 1999–2006 cars, and we rate it major. Putting it right costs $400 to $1,300 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 14 documented faults on the Chevrolet Silverado.
- Vehicle
- Chevrolet Silverado
- Years
- 1999–2006
- System
- Transmission
What you are looking at
No photograph available
What goes wrong
4WD GMT800 trucks with the push-button Autotrac system use the NP246 transfer case, whose electric encoder motor shifts between 2WD, Auto 4WD, 4HI and 4LO. The encoder motor and its encoder ring wear or corrode, triggering the Service 4WD message, codes such as C0306 and C0327, wrong mode lights, or a transfer case that refuses to change range. A truck sold as 4WD can be stuck in 2WD or stuck in 4WD. The motor bolts to the outside of the transfer case, so the repair is usually a part and an hour or two of labour, though a failed front axle actuator or control module can also cause the light.
What you would notice
- 'Service 4WD' warning light or message
- 4WD mode buttons flash or show the wrong mode
- Transfer case will not change into 4HI or 4LO
- Front wheels not driving in 4WD
How to check it
Where to look. Electric encoder motor bolted to the rear of the transfer case, under the truck behind the transmission
Look for a Service 4WD message or flashing 4WD button lights when the engine starts.
On a gravel or grass area, stop, try each mode button in turn (Auto 4WD, 4HI, then 4LO with the truck in neutral and foot on the brake), and check each light goes solid within a few seconds and the truck drives normally in each.
Feel for the front wheels pulling on a tight turn on gravel in 4HI.
Ask when the 4WD was last used and whether any transfer case parts have been replaced.
If a workshop inspection is possible: have the transfer case codes read with a scan tool (C0306, C0327 and similar) and the encoder motor connector checked for corrosion.
What it costs to put right
$400 to $1,300 at New Zealand independent workshop rates. That is for this job on its own, not for the car.
Ask the seller
- “Does the 4WD work in every mode?”
- “Has the Service 4WD light ever come on?”
- “Has the transfer case motor or control module been replaced?”
Now check the Chevrolet Silverado you are actually looking at
Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.
Where this comes from
- TahoeYukonForum thread 'NP 246 pinout?' (Service 4WD, C0327 encoder fault, encoder ring 88962315)
- Transmission Digest 'Up To Standards' (NP246 encoder motor operation)
- GM-Trucks.com GMT800 transfer case and Service 4WD discussions
Chevrolet Silverado buyer questions
Is transfer case encoder motor failure with 'service 4wd' light (np246 autotrac) serious on a Chevrolet Silverado?
We rate it major and common on the Chevrolet Silverado. 4WD GMT800 trucks with the push-button Autotrac system use the NP246 transfer case, whose electric encoder motor shifts between 2WD, Auto 4WD, 4HI and 4LO. The encoder motor and its encoder ring wear or corrode, triggering the Service 4WD message, codes such as C0306 and C0327, wrong mode lights, or a transfer case that refuses to change range. A truck sold as 4WD can be stuck in 2WD or stuck in 4WD. The motor bolts to the outside of the transfer case, so the repair is usually a part and an hour or two of labour, though a failed front axle actuator or control module can also cause the light.
How much does it cost to fix on a Chevrolet Silverado?
$400 to $1,300 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.
Which Chevrolet Silverado years are affected?
Our research records this fault on the 1999–2006 Chevrolet Silverado. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.
How do I check for it before I buy?
Look for a Service 4WD message or flashing 4WD button lights when the engine starts. On a gravel or grass area, stop, try each mode button in turn (Auto 4WD, 4HI, then 4LO with the truck in neutral and foot on the brake), and check each light goes solid within a few seconds and the truck drives normally in each. Feel for the front wheels pulling on a tight turn on gravel in 4HI. Ask when the 4WD was last used and whether any transfer case parts have been replaced. If a workshop inspection is possible: have the transfer case codes read with a scan tool (C0306, C0327 and similar) and the encoder motor connector checked for corrosion. Look here: Electric encoder motor bolted to the rear of the transfer case, under the truck behind the transmission