B0770 on 2015-2016 Chevrolet Colorado: Service 4WD Light Causes and Fixes

What's Unique About the 2015-2016 Chevrolet COLORADO

The 2015-2016 Chevrolet Colorado and its twin, the GMC Canyon, are particularly known for this issue. General Motors released Technical Service Bulletin #PIP5256B specifically acknowledging that the original factory-installed 4WD selector switch can be faulty or incorrect for the vehicle's configuration, leading directly to code B0770. For example, a 2015 Colorado should not have an 'Auto 4WD' position; if a switch with that option is installed, selecting it sends an invalid voltage to the TCCM and sets the code. This makes it a well-documented pattern failure on this platform, not a random electrical problem.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• "Service 4WD" message displayed on the instrument cluster.
• Inability to change 4WD modes (e.g., stuck in 2WD or 4WD).
• Indicator lights on the 4WD selector switch are not illuminated, do not change when the knob is turned, or perform a bulb check at startup and then go out.
• The 4WD system may be disabled as a precaution by the TCCM.

Most Likely Causes

1. Faulty or Incorrect Transfer Case Selector Switch 🔴 High Probability The original switch is a known high-failure part, as documented by GM in TSB #PIP5256B. Some vehicles were shipped with the incorrect switch from the factory. For instance, a 2015-2016 gas-engine Colorado should not have an 'Auto 4WD' mode, and installing a switch with that position will cause code B0770.
   How to confirm: The presence of code B0770 with a 'Service 4WD' message is the strongest indicator. If the lights on the switch are out and it doesn't respond, the switch has almost certainly failed. Visually confirm the switch in your truck matches the options your vehicle should have (e.g., no 'Auto' mode for most Colorados).
   Typical fix: Replace the transfer case selector switch assembly on the dashboard. This is a simple plug-and-play part that can be replaced in under 30 minutes.
   Est. part cost: $25-$50

Rare But Worth Checking

• Wiring Harness or Connector Issue: A poor connection, corrosion in the connector, or a damaged wire between the switch and the Transfer Case Control Module (TCCM) can mimic a failed switch. On Reddit, one owner reported their issue was a wire short in the harness near the parking brake. This is worth checking if a new switch doesn't solve the problem, but it is much less common than a failed switch.
• Faulty Transfer Case Control Module (TCCM): While possible, a failed TCCM is rare. In some cases, a TCCM software glitch can cause this, requiring a reflash by a dealer. However, the selector switch should always be considered the primary suspect before condemning the more expensive control module.

Diagnosis Steps

1. Use an OBD-II scanner capable of reading Body (B) and Chassis (C) codes to confirm B0770 is present. Standard scanners may not read these codes.
2. Verify the primary symptoms: 'Service 4WD' message is on, and the 4WD system is unresponsive.
3. Observe the 4WD selector switch. Turn the key to the 'ON' position. The switch indicator lights should perform a bulb check. If they are dead or don't respond when you turn the knob, the switch is the likely culprit.
4. Carefully pry the trim panel containing the switch away from the dashboard. It is typically held in by clips. A non-marring trim tool is recommended.
5. Inspect the electrical connector on the back of the switch for loose pins, corrosion, or damage. The connector has a small locking tab that must be released.
6. If the connector looks good, the most straightforward and cost-effective next step is to replace the switch.
7. After replacing the switch, clear the codes with the scanner and cycle the key. Test all 4WD modes to ensure proper operation. In many cases, simply starting the truck with the new switch installed will clear the 'Service 4WD' message automatically.

Parts You'll Likely Need

• Transfer Case Selector Switch (OEM #23135995) — This is the known high-failure component for code B0770 on this vehicle, as confirmed by GM's Technical Service Bulletin #PIP5256B. Note that multiple part numbers exist depending on the vehicle's options (with or without 'Auto 4WD'). Always verify the correct part for your VIN.
  Trusted brands: ACDelco (OEM), Dorman (e.g., 901-060)
  OEM price range: $35-$50
  Aftermarket price range: $25-$40

Related Codes That Often Appear With This One

• B2725 — This code for 'ATC/4WD Switch Circuit Malfunction' is also mentioned in TSB #PIP5256B. Both B0770 and B2725 point directly to a problem with the same 4WD selector switch assembly.

Technical Service Bulletins (TSBs) & Recalls

• PIP5256B: Addresses a 'Service 4WD' message and codes B0770 or B2725, identifying the cause as a faulty or incorrect Transfer Case Select switch and recommending its replacement. It specifies which models should and should not have the 'Auto 4WD' position on the switch.

Platform-Specific Known Issues

• Technical Service Bulletin #PIP5256B was issued by GM for the 2015-2016 Colorado and Canyon due to a 'Service 4WD' message with code B0770 or B2725. The bulletin states that some vehicles may have been built with the incorrect Transfer Case Select switch. For example, a 2015 Colorado does not have an 'Auto 4WD' option, and if a switch with that position is installed, the code will set. The fix is to replace it with the correct part for the vehicle's build.
• The issue is so common that many owners on forums diagnose it immediately as the switch, often citing the TSB.

Mechanic-Grade Diagnostic Values

• 5-Volt Reference Circuit Voltage at Switch Connector — expected: 4.5-5.5 V. Failure: A voltage greater than 5.5V suggests a short to voltage. A voltage less than 4.5V suggests an open or short to ground in the circuit or a faulty TCCM.
• AWD Indicator Control Circuit Voltage (Indicator Commanded OFF) — expected: Greater than 1.6 V. Failure: A voltage of 1.6 V or less for 1.5 seconds indicates a short to ground or an open/high resistance, setting code B0770 06.
• AWD Indicator Control Circuit Voltage (Indicator Commanded ON) — expected: Less than 3.4 V. Failure: A voltage of 3.4 V or greater indicates a short to battery, setting code B0770 01.
• Resistance between Indicator Dimming Control Circuit and all other pins at the switch connector — expected: Greater than 10 ohms. Failure: Resistance less than 10 ohms indicates the circuits are shorted together within the switch assembly.

Hidden / Shadow Codes Worth Checking

• B0770 01: AWD Indicator Circuit Short to Battery. The TCCM detects that the voltage on the indicator control circuit is too high (3.4V or greater) when the indicator is commanded ON. (see via Requires a scan tool capable of reading GM-specific body codes and their symptom bytes, such as a Tech2 or GDS2.)
• B0770 06: AWD Indicator Circuit Short to Ground or Open. The TCCM detects that the voltage on the indicator control circuit is too low (1.6V or less) when the indicator is commanded OFF. (see via Requires a scan tool capable of reading GM-specific body codes and their symptom bytes, such as a Tech2 or GDS2.)

Scan Tool Commands That Help

• GDS2 / Tech2: TCCM Data Display & Output Controls — Use this function to monitor the transfer case switch position in real-time as you turn the knob. You can also command the indicator lights on and off to test the circuit integrity, bypassing the physical switch. This helps determine if the fault is in the switch, wiring, or the TCCM itself.

Wiring & Ground Locations

• TCCM (Transfer Case Control Module) — Under the driver's seat, beneath the carpet. This location makes it susceptible to moisture damage from wet boots, snow, or water crossings, which can lead to corrosion and module failure.. The TCCM is the computer that reads the selector switch and controls the 4WD system. All wiring from the switch terminates here. Water damage to the module or its connectors can cause this code.
• SP106 (Ground Splice Pack) — On the passenger side of the engine bay, behind the engine airbox.. This ground splice pack serves the Transfer Case Control Module (TCCM) and the selector switch. Poor grounding at this point due to corrosion is a known GM issue and can cause erratic behavior and codes from the TCCM.
• Passenger Compartment Fuse Block — Behind a small door on the passenger side right kick panel.. This fuse block contains fuses relevant to the TCCM and other interior modules. A poor connection or blown fuse here could cause a loss of power or communication.

Real Owner Repair Stories

• tahoeyukonforum.com user 'Doubeleive' (GMC/Chevrolet Truck (specific model not mentioned, but system is analogous)) — Codes B0770, B0775, B0780, B0785 appeared on a scan.
  ❌ Tried (didn't work) Initial diagnosis was uncertain between a bad switch and a crushed harness.
  ✅ What actually fixed it The owner ordered a new switch from Rock Auto, which resolved the issue. The primary symptom was that the yellow indicator light for the selected mode was not illuminating.

Model Year Variations Within This Range

• 2015-2016: The correct 4WD selector switch depends on the RPO code for the transfer case. RPO NQ6 ('Autotrac') includes an 'Auto 4WD' position, while RPO NQ7 (standard part-time) does not. Installing a switch with an 'Auto' position in a vehicle without that feature is a direct cause of code B0770, as noted in TSB #PIP5256B.