P0706 on 2015-2016 Chevrolet Silverado 2500HD: Transmission Range Sensor Causes and Fixes

What's Unique About the 2015-2016 Chevrolet Silverado 2500HD

For the 2015-2016 Silverado 2500HD, a key distinction is that the Transmission Range Sensor is an internal component for both the 6L90 (gas) and Allison 1000 (diesel) transmissions. This makes replacement a significantly more involved job requiring removal of the transmission pan and valve body. While wiring issues are possible, as noted in TSB 21-NA-149 for later models, the internal location of the switch itself makes it a common failure point due to constant exposure to heat and transmission fluid. The NHTSA complaints citing P0706 alongside other transmission and U-codes on similar GM vehicles suggest that a wiring inspection is still a critical diagnostic step before committing to an internal transmission repair.

Symptoms You May Notice

• Check Engine Light is on
• Vehicle will not start, especially in Park or Neutral.
• Inability to shift the gear lever out of Park.
• Delayed or harsh gear engagement.
• Vehicle may start in a gear other than Park or Neutral.
• Incorrect or blank gear indicator on the dashboard.
• Transmission enters 'limp mode'.
• 'Shift Range Inhibited' message on the driver information center.
• Reverse lights do not illuminate.

Most Likely Causes

1. Faulty Internal Transmission Range Sensor (NSBU Switch) 🔴 High Probability The sensor is located inside the transmission, submerged in fluid and exposed to constant heat cycles. Over time, the internal electronics or contacts fail. This applies to both the 6L90 (gas) and Allison (diesel) transmissions in this year range.
   How to confirm: Use a scan tool to monitor the transmission range data while shifting. If the displayed gear is erratic, does not match the shifter's position, or shows an invalid reading, the sensor is the primary suspect. This confirms an internal fault, as external wiring issues would typically present differently.
   Typical fix: Replace the internal sensor. This is a labor-intensive job that involves draining the transmission fluid, removing the transmission pan, and then removing the valve body to access and replace the sensor. The valve body must be carefully reinstalled and torqued to specification.
   Est. part cost: $40-$210
2. Damaged Wiring or Corroded Connector 🟡 Medium Probability The main transmission harness connector can accumulate dirt and moisture, leading to corrosion. The harness itself can be damaged by heat from the exhaust or chafing against the frame, causing shorts or open circuits. This is a known issue on some GM truck platforms.
   How to confirm: Visually inspect the main electrical connector at the transmission case for corrosion or pushed-out pins. Trace the harness as far as possible, looking for signs of melting, chafing, or breaks. Perform a continuity test on the signal wires between the external transmission connector and the TCM connector.
   Typical fix: Repair the damaged section of the wiring harness. Clean any corrosion from the connector pins using an electrical contact cleaner and apply dielectric grease to prevent future moisture intrusion.
   Est. part cost: $10-$50
3. Misadjusted Shift Linkage ⚪ Low Probability
   How to confirm: Check if the gear indicator on the dash correctly aligns with every shifter position. If there is excessive play in the shifter cable or the indicator is consistently off, the linkage may be out of adjustment, causing the internal sensor to read between gears.
   Typical fix: Adjust the shift cable at the transmission lever. This ensures the manual valve inside the transmission is correctly positioned for each gear selection, allowing the range sensor to send a clear signal.
   Est. part cost: $0

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): This is rare, but if the sensor and wiring are confirmed to be good, the TCM's internal driver circuit for the range sensor may have failed. This is more likely if multiple other transmission codes are present and communication with the TCM is intermittent.

Diagnosis Steps

1. Connect an OBD-II scanner and confirm the presence of P0706. Note any other codes, especially P0700 or U-codes.
2. Using the scanner's live data function, monitor the Transmission Range Sensor parameter. Slowly move the gear shifter through all positions (P, R, N, D, L) and verify that the sensor reading on the scanner matches the shifter position.
3. If the reading is incorrect, erratic, or shows 'Invalid', the problem is very likely internal to the transmission (the sensor itself).
4. If the reading is stable but incorrect (e.g., shows Neutral when in Drive), inspect the shift linkage for looseness or misadjustment.
5. Perform a thorough visual inspection of the main transmission wiring harness and its connector. Look for any signs of physical damage, melting near the exhaust, or green corrosion in the connector pins.
6. If wiring appears damaged, repair the affected section.
7. If the wiring and shift linkage are confirmed to be good, the fault is almost certainly the internal Transmission Range Sensor.
8. Replacement of the internal sensor is an advanced repair. If you are not comfortable with removing the transmission pan and valve body, seek professional service.

Parts You'll Likely Need

• Transmission Range Sensor / Neutral Safety Switch (for 6L90 Gas) (OEM #24259032) — This is the internal sensor for the 6L90 transmission used with the 6.0L gas engine. It is the most common component to fail and cause P0706.
  Trusted brands: ACDelco, GM Genuine Parts, Dorman
  OEM price range: $60-$100
  Aftermarket price range: $40-$70
• Neutral Safety Back-Up (NSBU) Switch (for Allison 1000 Diesel) (OEM #29542692) — This is the internal range sensor for the Allison transmission used with the 6.6L Duramax engine. Failure causes P0706 and often a 'Shift Range Inhibited' message.
  Trusted brands: Allison Transmission (OEM), ACDelco
  OEM price range: $150-$210
  Aftermarket price range: $90-$140

Related Codes That Often Appear With This One

• P0700 — P0700 is a general code indicating that the Transmission Control Module (TCM) has detected a fault. It almost always accompanies specific transmission codes like P0706.
• P0705 — This code indicates a malfunction in the entire sensor circuit, while P0706 points to a performance/range issue. They often appear together as they relate to the same component.
• U-codes — The presence of communication codes (U-codes) alongside P0706, as seen in NHTSA complaints, strongly suggests a wiring harness issue or a failing module is disrupting communication between the TCM and other vehicle systems.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-149: While this TSB applies to 2019+ models, it documents a widespread issue of engine wiring harness chafing causing various DTCs. It highlights a diagnostic pattern (multiple codes, communication errors) that can be relevant to troubleshooting similar issues on 2015-2016 models.
• N182188930: This is a Special Coverage bulletin for 2017-2018 models addressing leaking transmission cooler lines due to rubbing. While outside the 2015-2016 range, it points to a known weak spot in the GM HD truck platform that owners of all years should be aware of, as fluid loss can cause severe transmission problems.

Platform-Specific Known Issues

• For models equipped with the Allison 1000 transmission (6.6L Duramax), the part is specifically called the Neutral Safety Back-Up (NSBU) switch, GM/Allison P/N 29542692. It is located inside the transmission and requires valve body removal to replace.
• For models equipped with the 6L90 transmission (6.0L Gas), the part is called the Transmission Range Sensor, GM P/N 24259032. It is also located inside the transmission, attached to the valve body, and requires the same labor-intensive procedure to replace.

Hidden / Shadow Codes Worth Checking

• P1709-P1714, P840-P876: These are pressure manifold switch codes. On Allison transmissions, the Pressure Switch Manifold (PSM) and the NSBU switch cross-check each other's readings. The presence of these codes along with P0706 can strongly point to a faulty NSBU switch providing conflicting information to the TCM. (see via A professional scan tool like a GM GDS2 or Tech 2 that can read manufacturer-specific transmission codes.)

Scan Tool Commands That Help

• GDS2/Tech 2: Transmission Data Display — This is the primary diagnostic screen for this fault. It allows a technician to view the state (High/Low or On/Off) of the individual signal circuits from the range sensor in real-time while moving the shifter. An invalid or illogical combination of signals that doesn't correspond to a valid gear position confirms a fault in the sensor or its wiring.
• GDS2/Tech 2: TCM-to-sensor handshake / Communication Check — If the sensor and wiring appear to be good, this bidirectional command can be used to test the TCM's ability to communicate with the sensor. A failure to receive a valid response can point towards an internal fault within the Transmission Control Module itself.

Real Owner Repair Stories

• gm-trucks.com forum user (2016 Chevrolet Silverado 2500HD with 6.0L Gas Engine) — Erratic shifting and a P0706 trouble code.
  ❌ Tried (didn't work) Initial diagnosis was uncertain due to the internal nature of the sensor.
  ✅ What actually fixed it A repair shop diagnosed a failed internal transmission range sensor. The fix required dropping the transmission pan and the valve body to access and replace the sensor (P/N 24259032). The total repair cost was approximately $850.

OEM Part Supersession History

• 29540479 → 29542692 — Updated design for improved durability and resistance to moisture intrusion. The original black switch was known for higher failure rates.
  Heads up: The older black switch should not be used. The updated tan or gray switch (29542692) is the correct, more robust replacement.

Model Year Variations Within This Range

• 2016: The 2016 model year received a facelift with a new hood, headlights, and grille. Technologically, it gained support for Apple CarPlay/Android Auto and an optional wireless charging pad. However, for the 2500HD models, the core powertrain, including the 6.0L/6L90 and 6.6L/Allison 1000 combinations, remained unchanged from 2015. The P0706 diagnosis is identical for both years.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Catastrophic CP4 High-Pressure Fuel Pump Failure (Duramax LML) 🔴 High — A widely documented issue affecting 2011-2016 Duramax LML engines. Failure can occur without warning and causes metal debris to contaminate the entire fuel system, leading to repairs often exceeding $10,000.
• Leaking Transmission Cooler Lines 🟠 Medium — The factory crimps on the flexible sections of the transmission cooler lines are a common failure point, leading to fluid leaks. This issue is common enough that GM issued a special coverage program (N182188930) for later models (2017-2018) with a similar problem. (Ref: N182188930 (for later models, but highlights the known problem area))
• Infotainment System Glitches ('Phantom Touch' / Blank Screen) 🟡 Low — Owners report issues with the MyLink infotainment screen freezing, going blank, or registering 'phantom' touches. Sometimes this can be temporarily fixed with a system reset or by disconnecting the battery. In other cases, the digitizer screen itself fails and requires replacement.
• Brake Pedal Pivot Nut Loosening 🔴 High — A recall was issued for 2015-2016 models because the brake pedal pivot nut could loosen, potentially causing the brake pedal to become loose or inoperative. (Ref: GM Recall #20760)
• DEF System Problems (Duramax LML) 🟠 Medium — Issues with the Diesel Exhaust Fluid (DEF) system, including faulty sensors and heaters, are common. These can lead to 'limp mode' or no-start conditions if not addressed.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, purchasing a used internal transmission range sensor is NOT recommended. It is a high-failure electronic component located inside the transmission, and the labor cost to replace it is very high. The risk of a used part failing shortly after installation outweighs any potential cost savings.

What to inspect on the donor part:

• Not applicable, as used parts are not advised for this repair.

OEM-only on this vehicle (don't cheap out):

• Transmission Range Sensor / NSBU Switch: Given the critical function and high labor cost for replacement, using an OEM part from GM, ACDelco Professional, or Allison is strongly recommended for reliability.

Aftermarket brands forum-validated for this vehicle:

• ACDelco Professional
• Allison Transmission (for Duramax models)

Brands owners have reported issues with on this vehicle:

• Dorman: While Dorman offers a replacement, forum discussions and mechanic reviews frequently cite inconsistent quality and higher failure rates for their electronic components compared to OEM. Given the labor-intensive nature of this repair, avoiding lower-quality parts is a wise investment.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0700 — A general transmission control system malfunction code that often accompanies P0706 to alert the ECM that the TCM has detected a fault.
• U0001 — Communication codes (U-codes) can appear alongside P0706 if the issue is related to wiring harness chafing or connector corrosion as noted in TSB 21-NA-149.

Frequently Asked Questions