P0843 on 2006-2010 GMC Sierra: Transmission Pressure Sensor Causes and Fixes

What's Unique About the 2006-2010 Gmc SIERRA

The 2006-2010 Sierra spans two truck generations with different transmissions, which completely changes the repair. The 2006 GMT800 models with the 4L60-E/4L65-E transmission have a relatively simple, replaceable pressure manifold switch. In contrast, the 2007-2010 GMT900 trucks with the 6L80 transmission have the pressure switches integrated into the entire control module (TEHCM), making the repair significantly more complex and costly as the whole unit often needs replacement and programming.

Diagnostic Flowchart

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

Generation note: This range covers the end of the first generation (GMT800, 2006 model year) and the beginning of the second generation (GMT900, 2007-2010). The GMT800s typically use a 4-speed automatic (4L60-E/4L65-E), while the GMT900s use a 6-speed (6L80). The cause and repair for P0843 are different between these transmissions.

Symptoms You May Notice

• Check Engine Light or transmission warning light is on
• Harsh, banging, or delayed gear shifts
• Transmission is stuck in a single gear (limp mode), often 3rd gear
• Inability to shift into certain gears
• Loss of reverse gear
• Engine RPMs flare between shifts

Most Likely Causes

1. Failed Transmission Electro-Hydraulic Control Module (TEHCM) 🔴 High Probability → Shop Transmission Assembly Applies to 2007-2010 models with the 6L80 6-speed transmission. The pressure switches are thin membranes integrated into the TEHCM, which is a known failure point due to cracking from heat and vibration. 🎬 See how to repair the 6L80 pressure switch membranes.
   How to confirm: A professional scan tool will show the data for pressure switch 'A' is stuck high or open and does not change when gears are commanded.
   Typical fix: Replace the entire TEHCM and valve body assembly. The new module must be programmed to the vehicle.
   Est. part cost: $400-$800
2. Failed Transmission Fluid Pressure (TFP) Manifold Switch 🔴 High Probability → Shop Transmission Assembly Applies to 2006 models with the 4L60-E/4L65-E 4-speed transmission. This switch assembly is a common failure item located inside the transmission pan.
   How to confirm: After dropping the transmission pan, the switch can be tested for electrical continuity. A diagnostic scan tool will also show an invalid reading for the switch that doesn't change with gear selection.
   Typical fix: Drop the transmission pan, remove the old pressure manifold switch from the valve body, and install a new one. 🎬 Watch: 4L60-E manifold pressure switch common issues and service walkthrough. A transmission filter and fluid change is required as part of the job.
   Est. part cost: $70-$150
3. Damaged Wiring or Corroded Connector ⚪ Low Probability The main transmission harness connector, located on the driver's side of the transmission, can be exposed to moisture and road debris, leading to corrosion. Wires can also chafe against the chassis or engine components.
   How to confirm: Visually inspect the wiring harness leading to the transmission for any signs of damage, melting, or corrosion at the main connector. Test for continuity and voltage at the connector pins.
   Typical fix: Repair the broken/shorted wire or clean/replace the corroded connector.
   Est. part cost: $10-$50
4. Dirty or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly This is not a direct cause, but a major contributing factor. Metallic debris from normal wear, especially from the torque converter clutch, contaminates the fluid and can damage the delicate pressure switch diaphragms on the 6L80 TEHCM.
   How to confirm: When the pan is dropped, inspect the fluid and pan magnet for excessive metal shavings. Dark, burnt-smelling fluid indicates a larger mechanical issue.
   Typical fix: A fluid and filter change is required with the component replacement, but will not fix the P0843 code by itself.
   Est. part cost: $70-$150

Rare But Worth Checking

• Faulty Transmission Control Module (TCM) or Powertrain Control Module (PCM): → Shop Transmission Assembly This is very rare. The module should only be suspected after all other possibilities, including the internal transmission components and wiring, have been definitively ruled out. On 6L80 models, the TCM is integrated into the TEHCM, so a faulty TCM is resolved by replacing the TEHCM.

Diagnosis Steps

1. Connect a professional-grade scan tool capable of reading transmission live data.
2. Check for any other stored transmission codes. If P0700 is present, it confirms a TCM fault; P0843 is the specific issue.
3. Observe the live data for Transmission Fluid Pressure Switch 'A'. The reading will likely be stuck high or show an open circuit status.
4. If possible, command different gears using the scan tool and verify that the status of switch 'A' does not change.
5. Inspect the main transmission wiring harness and connector for any visible damage, corrosion, or loose pins.
6. If wiring appears intact, the next step is to drop the transmission pan for internal inspection.
7. For 2006 models (4-speed), inspect and replace the TFP manifold switch. It is recommended to also replace the internal harness as it becomes brittle.
8. For 2007-2010 models (6-speed), inspect and replace the TEHCM assembly.
9. After replacement, fill with new DEXRON-VI transmission fluid, install a new filter, clear the codes, and perform a test drive. For TEHCM replacement, programming is required before the test drive.

Parts You'll Likely Need

• Transmission Electro-Hydraulic Control Module (TEHCM) (OEM #24256861) — This is the most common fix for 2007-2010 models with the 6L80 transmission, as the pressure switches are integrated into this unit. Note: This part has faced significant supply shortages.
  Trusted brands: ACDelco (GM Original Equipment), Dorman (e.g., 609-000)
  OEM price range: $500-$800
  Aftermarket price range: $400-$650
• Transmission Fluid Pressure (TFP) Manifold Switch (OEM #24229843) — This is the most common fix for 2006 models with the 4L60-E/4L65-E transmission.
  Trusted brands: ACDelco, ATP Automotive, Standard Motor Products (SMP)
  OEM price range: $100-$150
  Aftermarket price range: $70-$120
• Transmission Filter and Pan Gasket Kit — Required for any repair that involves dropping the transmission pan. Use only DEXRON-VI fluid for 6L80 transmissions.
  Trusted brands: ACDelco, Wix, Fram
  OEM price range: $40-$70
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0700 — This is a generic code that simply means the Transmission Control Module (TCM) has stored a fault. It will almost always be present alongside a specific transmission code like P0843.
• P0751, P0756, P0776, P0877, P2715 — On 6L80 transmissions (2007-2010), the pressure switches and solenoids are part of the same TEHCM assembly. A failing module can cause multiple circuit faults for both switches and solenoids simultaneously. The NHTSA TSB #PIP4379K also lists these codes together.

Technical Service Bulletins (TSBs) & Recalls

• PIP4379K: Groups P0843 with numerous other transmission codes (P0701, P0731, P0751, etc.) related to range inhibit or no reverse conditions, suggesting a common point of failure like the TEHCM. This TSB instructs technicians to follow diagnostics for P0701 first when multiple codes are present.

Platform-Specific Known Issues

• 6L80 TEHCM Membrane Failure: → Shop Transmission Valve Body The pressure switches inside the 6L80 TEHCM are not traditional sensors but thin, flexible membranes laminated onto a circuit board. Over time, the constant exposure to hot transmission fluid and pressure cycles causes these membranes to crack or delaminate. This breach creates an open circuit, which the TCM interprets as a 'Circuit High' voltage, triggering P0843.

Mechanic-Grade Diagnostic Values

• TFP Sensor/Switch 'A' Signal Voltage (6L80) — expected: 0.5V (low pressure) to ~4.5V (high pressure). Failure: A sustained reading above 4.5V-4.8V, often stuck at 5.0V, indicates a 'Circuit High' fault.
• TEHCM Regulated Voltage Supply (6L80) — expected: 8.3 - 9.3 Volts. Failure: Voltage outside this range could indicate a fault in the TEHCM's internal power regulation.
• TFP Pressure Switch Resistance (4L60-E, no pressure) — expected: ~0.7 - 1.9 Ohms. Failure: Infinite resistance (OL) indicates a failed, open switch, which causes the 'Circuit High' code.
• 6L80 TEHCM Pressure Switch State (No Pressure) — expected: Closed Circuit (Continuity). Failure: An open circuit (no continuity) when no pressure is applied indicates a failed switch.
• 6L80 TEHCM Pressure Switch State (Pressure Applied) — expected: Open Circuit (No Continuity). Failure: Remaining a closed circuit under pressure indicates a stuck switch.

Scan Tool Commands That Help

• GDS2 / Tech 2: Solenoid Valve State Control / Output Control — Used to command individual solenoids and gears while monitoring the live data for the TFP switches. For P0843, a technician would command shifts and watch to see if TFP Switch 'A' changes state. If it does not change from its 'High' or 'Open' status, the switch or its circuit within the TEHCM is confirmed as faulty.
• GM SPS2 / Techline Connect: Module Reprogramming — This is a mandatory step after installing a new TEHCM. The module must be programmed with the vehicle's specific VIN and calibration files before it will function.

Real Owner Repair Stories

• DuramaxDiesels.com forum member (2009 GMC with Allison Transmission (similar control architecture)) — Sporadic P0751 and P0843 codes, transmission entering limp mode, especially during long idles or trips.
  ❌ Tried (didn't work) Replacing the Pressure Switch Manifold (PSM), Replacing the internal transmission wiring harness, Checking continuity on the external wiring harness
  ✅ What actually fixed it The problem was ultimately resolved by replacing the entire valve body with a rebuilt unit, suggesting a stuck shift valve or an internal hydraulic leak within the valve body itself was the root cause, not just the electrical components.

OEM Part Supersession History

• 24256861 (TEHCM for 6L80) → 19431596 — The original TEHCM part number 24256861 faced a major, multi-year supply shortage. GM eventually released an upgraded, replacement part number.
  Heads up: TEHCMs are year-specific and not interchangeable; installing the wrong year or part number can result in a no-start or immediate limp mode condition. The module must be programmed to the vehicle's VIN.

Model Year Variations Within This Range

• 2007-2010 (6L80): While the core failure of the TEHCM pressure switch membranes is common across these years, GM made several internal revisions to the TEHCM hardware and software. Early Gen 1 TEHCMs (approx. 2007-2008) are known to be more prone to pressure switch issues. Later versions featured improved solenoids and updated logic. It is critical to match the TEHCM Tag ID and year when ordering a replacement, as they are not always interchangeable.