P0848 on 2006-2010 Chevrolet Silverado: Transmission Pressure Switch 'B' Circuit High Causes and Fixes

What's Unique About the 2006-2010 Chevrolet SILVERADO

The 2006-2010 Silverado spans two generations (GMT800 'Classic' and GMT900) and two common transmissions: the 4-speed 4L60E and the 6-speed 6L80. The cause of P0848 is different for each. On the more common 6L80, the issue is almost always the failure of small, fragile rubber diaphragms on the internal Transmission Electro-Hydraulic Control Module (TEHCM). These are a well-documented weak point that become brittle and tear. For the 4L60E, the cause is typically the entire manifold pressure switch assembly failing electrically.

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 GMT800 platform (sold as 'Classic' models in 2007) and the GMT900 platform (2007-2010). The GMT800s more commonly used the 4-speed 4L60E, while the GMT900s, particularly from 2009 onward with V8 engines, primarily used the 6-speed 6L80. Identifying the transmission is the first step in diagnosis. Check the RPO code sticker in the glove box: M30 for 4L60E, MYC for 6L80.

Symptoms You May Notice

• Check Engine Light or transmission warning light is on.
• Harsh, erratic, or delayed shifting, especially a harsh 1-2 shift.
• Transmission is stuck in one gear (limp mode), often 3rd gear.
• Vehicle may not move in forward or reverse, or may go into neutral unexpectedly, as mentioned in TSB PIP4379M.
• Poor acceleration and reduced fuel economy.
• Torque converter clutch (TCC) may be inhibited from engaging.

Most Likely Causes

1. Failed Pressure Switch Diaphragm on TEHCM (6L80 Transmission) 🔴 High Probability → Shop Transmission Valve Body The rubber diaphragms on the TEHCM (Transmission Electro-Hydraulic Control Module) inside the 6L80 transmission are a well-documented failure point. They become brittle with age and heat cycles, eventually tearing and causing an open circuit which the TCM reads as high voltage.
   How to confirm: After dropping the transmission pan, the valve body and TEHCM assembly must be removed. A visual inspection will reveal torn, dislodged, or perforated orange or black diaphragms on the TEHCM plate. Often, multiple diaphragms will be found torn. The switches are normally closed and open under pressure; a torn diaphragm prevents this, leaving the circuit open (high).
   Typical fix: Replace the failed diaphragms using an aftermarket repair kit (e.g., Sonnax 124740-30K or TransGo PSR-5). This is much cheaper than replacing the entire TEHCM assembly, which requires expensive VIN programming. 🎬 Watch: How to reseal the 6L80 pressure switches yourself. A special tool is often included or required to properly install the new seals and diaphragms without damage.
   Est. part cost: $50-$150
2. Failed Transmission Fluid Pressure (TFP) Manifold Switch (4L60E Transmission) 🔴 High Probability → Shop Transmission Assembly The plastic manifold switch assembly mounted on the valve body is a common failure item on the 4L60E transmission. It can fail electrically internally or become clogged with metallic debris, leading to incorrect pressure readings.
   How to confirm: After dropping the transmission pan, the manifold switch can be tested for correct resistance with a multimeter. However, it is often replaced as the primary suspect once external wiring is ruled out due to its high failure rate. Visually inspect for contamination on the switch screens.
   Typical fix: Replace the entire TFP manifold switch assembly (ACDelco P/N: 24215111), 🎬 See this walkthrough on changing the 4L60E pressure switch. along with the transmission filter and pan gasket.
   Est. part cost: $60-$150
3. Damaged Wiring or Poor Connection 🟡 Medium Probability The main transmission harness connector can accumulate dirt and moisture, and wiring can be damaged by heat from the exhaust or road debris. The internal harness, constantly submerged in hot fluid, can also become brittle and crack over time.
   How to confirm: Visually inspect the external transmission connector for corrosion or pushed-out pins. Test the signal wire for a short to power or an open circuit between the TCM and the transmission connector. Inspect the internal harness for brittleness or damage when the pan is off.
   Typical fix: Clean the connector terminals or repair the damaged section of the wiring harness. If the internal harness is damaged, it must be replaced.
   Est. part cost: $10-$100

Rare But Worth Checking

• Faulty Transmission Control Module (TCM/TEHCM): → Shop Transmission Assembly This is rare. The TCM is the last part to suspect after confirming the sensor/switch and wiring are good. On 6L80 models, the TEHCM is the unit that contains the failure-prone diaphragms, but the module's circuit board itself rarely fails. If it does, a replacement must be programmed to the vehicle's VIN.
• Extremely Low or Contaminated Transmission Fluid: → Shop Transmission Assembly While low fluid typically causes slipping or other codes, it can lead to erratic pressure readings if the pump cavitates. A user on DuramaxDiesels.com with P0848 was advised to check the fluid level first as a preliminary step.

Diagnosis Steps

1. Check the transmission fluid level and condition. Address any low or burnt fluid first. On sealed transmissions, this must be done from underneath with the engine running.
2. Scan for all DTCs. Note if P0848 appears with other pressure switch codes, which is a strong clue for a component failure.
3. Identify the transmission model (4L60E or 6L80) using the RPO codes in the glove box (M30 or MYC).
4. Inspect the external transmission wiring harness and main connector for any visible damage, corrosion, or loose pins.
5. If external wiring is intact, drop the transmission oil pan and inspect for excessive metal debris, which would indicate a severe mechanical failure.
6. For 6L80 transmissions: Remove the valve body/TEHCM assembly and carefully inspect the pressure switch diaphragms for tears or holes. 🎬 Watch: How to bench test the 6L80 TEHCM electrical circuit. A YouTube video by 'Just a dude' shows this inspection process clearly.
7. For 4L60E transmissions: Remove and replace the manifold pressure switch (ACDelco 24215111) located on the valve body. While testing is possible, replacement is common practice due to high failure rates.
8. After replacing parts, install a new transmission filter and pan gasket, and refill with the correct fluid (DEXRON-VI).
9. Clear all codes and perform a transmission relearn drive cycle, driving smoothly through all gears to allow the TCM to adapt to the new components.

Parts You'll Likely Need

• TEHCM Pressure Switch Diaphragm Repair Kit — For the 6-speed 6L80 transmission, this kit allows for the replacement of just the failed rubber diaphragms on the TEHCM, which is the most common point of failure.
  Trusted brands: Sonnax (P/N: 124740-30K, includes tool and seals for one unit), TransGo (P/N: PSR-5)
  OEM price range: N/A
  Aftermarket price range: $50-$150
• Transmission Fluid Pressure Switch Manifold (OEM #24215111) — This is the most common fix for the 4-speed 4L60E transmission. It contains all the pressure switches in one assembly.
  Trusted brands: ACDelco (OEM), Dorman (92436)
  OEM price range: $80-$120
  Aftermarket price range: $50-$90
• Transmission Filter Kit (with Gasket) — This must be replaced anytime the transmission pan is removed for service.
  Trusted brands: ACDelco, Wix, ATP
  OEM price range: $30-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0701 — This is a general Transmission Control System Malfunction code. TSB #PIP4379K specifically advises diagnosing P0701 first when it appears with other transmission codes like P0848, as it can indicate a broader system issue.
• P0843, P0873, P0877, P2723 — These are codes for other transmission pressure switches ('A', 'C', 'D', 'E'). When multiple pressure switch codes appear together, it strongly points to a failure of the TEHCM diaphragms (on 6L80) or the manifold switch (on 4L60E), as these components house multiple switches. A forum user on SilveradoSierra.com reported P0848 and P0873 together, which was fixed by replacing the TEHCM laminated plate/seals.

Technical Service Bulletins (TSBs) & Recalls

• PIP4379K: Mentions P0848 as one of many possible DTCs related to transmission performance issues and advises diagnosing P0701 first if present.
• PIP5025E: A well-known TSB that addresses multiple DTCs and shift quality concerns on 6L80/6L90 transmissions, often pointing towards issues with the TEHCM, valve body, and pressure switches.

Platform-Specific Known Issues

• TSB #PIP4379K notes that P0848 can appear with a wide range of other transmission codes. It advises following the diagnostic procedure for code P0701 first if it is present, suggesting a potential for a broader control system fault.
• TSB #PIP5025E (and its revisions) also discusses various transmission codes, including pressure switch faults on 6L80 transmissions, often leading to the inspection of the TEHCM and its components.
• A real-world repair story on SilveradoSierra.com for an '11 Silverado with a 6.2L V8 and 6L80E showed codes P0848 and P0873. The owner fixed it by replacing the laminated plate with integrated seals on the TEHCM, avoiding a costly full TEHCM replacement.

Mechanic-Grade Diagnostic Values

• 4L60E Shift Solenoid (1-2 & 2-3) Resistance — expected: 20-40 Ohms. Failure: Reading outside this range indicates a faulty solenoid.
• 4L60E Pressure Control (PC) Solenoid Resistance — expected: 3.5-8.0 Ohms. Failure: Reading outside this range indicates a faulty PC solenoid.
• 6L80 TEHCM Pressure Switch State — expected: Normally Closed (shows continuity with no pressure). Failure: An open circuit (no continuity) at rest indicates a failed switch or torn diaphragm.
• Transmission Fluid Pressure Sensor/Switch Circuit Voltage — expected: Below 4.5V. Failure: A reading above 4.5V triggers the 'Circuit High' code.

Scan Tool Commands That Help

• Bidirectional Scan Tool (e.g., Tech2): Pressure Control Solenoid (PCS) Test — For 4L60E, this command allows a technician to vary the amperage to the PCS (0 to 1.1 amps) to see if it correctly regulates line pressure. This helps differentiate a mechanical pressure issue from an electrical control problem.
• GM SPS2 or Techline Connect: TEHCM Programming and Fast Learn/Reset Adapts — This is required after replacing the entire TEHCM on a 6L80 transmission. The module must be programmed to the vehicle's VIN, and a relearn procedure is necessary to ensure proper shift quality.

Wiring & Ground Locations

• G103 — On the front of the passenger side (right side) cylinder head on some GMT900 models. On others, it's on the cowl above the brake booster.. This is a primary ground for the Engine Control Module (ECM). A poor connection here can cause erratic sensor readings and 'circuit high' codes due to a floating ground.
• PCM Ground (GMT800) — A black wire with a white stripe that grounds to the top rear of the engine block.. This is the main ground for the Powertrain Control Module on GMT800 trucks. A loose or corroded connection here is a very common cause of numerous electrical issues, including sensor faults.
• Transmission Case Connector (X175) — The main round electrical connector on the passenger side of the transmission case.. This is the critical interface between the internal transmission electronics (pressure switches, TEHCM) and the vehicle's main harness. Corrosion or pushed-out pins here can directly cause an open circuit, leading to a P0848 code.
• TCM Connector (80-way) — At the Transmission Control Module (on models where it's separate from the TEHCM).. For diagnosing a 6L80, Pin 17 (Pink wire) is the signal circuit for Fluid Pressure Switch 1. Testing for voltage and continuity here is essential for external wiring checks.

Real Owner Repair Stories

• TahoeYukonForum.com user (2011 GMC Yukon XL (with 6L80 transmission)) — Check engine light with codes P0848 and P0873.
  ❌ Tried (didn't work) The user did not report trying other fixes first.
  ✅ What actually fixed it The user dropped the valve body and found the laminated discs/seals for the pressure switches were damaged. They replaced the seals (likely with a kit like the Sonnax 124740-30K) which resolved the codes.

OEM Part Supersession History

• 24241350 / 24252114 → 24256861 / 24256863 — Improved solenoids and an updated pressure manifold gasket to address common failures.
  Heads up: Early Gen 1 TEHCMs (2006-2009) are known for frequent pressure switch issues. The 2010+ modules are an improvement, but programming is always required when swapping.

Model Year Variations Within This Range

• 2006-2009: Silverados in this range with the 6L80 transmission used an early generation TEHCM (e.g., P/N 24241350) that was particularly prone to pressure switch failures.
• 2010: The 2010 model year introduced an updated TEHCM (e.g., P/N 24256861) with improved solenoids and gaskets, though the diaphragm design remained a potential failure point.