P2635 on 2017 GMC Sierra: Fuel Pump Low Flow Causes and Fixes

What's Unique About the 2017-2017 Gmc SIERRA

For this generation of GMC Sierra and its platform mates, the P2635 code is strongly linked to specific environmental conditions, as documented in official GM Technical Service Bulletins. In temperatures above 100°F (38°C), the code often points to vapor buildup in the fuel line, which the original-design fuel pump cannot overcome. Conversely, in very cold weather (below 20°F or -6°C), the code may appear alongside P018B, pointing towards a faulty fuel pressure sensor rationality check.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light (MIL) illuminated
• Hesitation or stumbling during acceleration.
• Engine surging.
• Stalling, especially in very hot weather, often in stop-and-go traffic.
• No-start or start-and-stall condition, particularly in very cold weather.
• Loss of power or entering 'limp mode'.
• Extended crank time before the engine starts.

Most Likely Causes

1. Failing In-Tank Fuel Pump Module 🔴 High Probability As per TSB #17-NA-335, the original fuel pump module may allow vapor buildup in the fuel feed line during high ambient temperatures (100°F+), leading to a drop in fuel flow and stalling. An updated pump module was released by GM to correct this design flaw, which features an improved one-way breather valve.
   How to confirm: Monitor low-side fuel pressure with a scan tool during the event. A significant drop in pressure during hesitation or stalling events, especially in hot weather, points to the pump. The issue may not be reproducible in a cool shop environment. The problem is often worse with less than a half tank of fuel.
   Typical fix: Replace the entire in-tank fuel pump module assembly with the updated GM part. 🎬 See a walkthrough of the fuel pump flow performance fix. TSB #PIP5411F lists specific updated part numbers based on the truck's configuration (e.g., wheelbase, cab size).
   Est. part cost: $350-$500
2. Faulty Low-Pressure Fuel Pressure Sensor 🟡 Medium Probability TSB #PIP5286B notes that the sensor may fail to read the low end of its range correctly, causing the ECM to set P2635 and P018B, particularly in cold weather. The sensor can get 'stuck' reading a certain pressure (e.g., 48.7 PSI) even when the system is depressurized.
   How to confirm: Use a scan tool to monitor the 'Low Side Fuel Pressure' PID. Per TSB #PIP5286B, with a cold engine, command the fuel system to depressurize. The sensor reading should drop to zero. If it remains at a higher value (e.g., 30-40 PSI) after the engine stalls, the sensor is faulty. This sensor is located on the frame rail under the driver's side of the vehicle.
   Typical fix: Replace the low-pressure fuel pressure sensor. The OEM part number is commonly GM #13516496 (superseding #13579380). Note: The O-ring seal is often not included and must be ordered separately.
   Est. part cost: $40-$80
3. Damaged Wiring or Connectors ⚪ Low Probability The Fuel Pump Control Module (FPCM) is located on the frame rail near the spare tire, exposing it and its connector to road salt, moisture, and debris, which can lead to corrosion and connection issues.
   How to confirm: Visually inspect the wiring harness and connector at the FPCM (under the rear of the truck) for green corrosion or physical damage. Also inspect the connector at the fuel pressure sensor on the frame rail. Use a multimeter to check for continuity and proper voltage at the pump and sensor connectors.
   Typical fix: Repair or replace the damaged section of the wiring harness or the faulty connector. In cases of heavy corrosion, the FPCM itself may need replacement. 🎬 Watch: How to locate and replace the fuel pump control module.
   Est. part cost: $20-$150

Rare But Worth Checking

• Fuel Pump Control Module (FPCM) Issue: While less common than the pump or sensor for this specific code, a failing FPCM can cause erratic fuel pump operation and trigger P2635. Symptoms can include intermittent no-starts, stalling when hot, and long crank times. Its location under the truck makes it prone to moisture damage.
• Network Communication Fault: TSB #PIP5427B mentions that P2635 can be set alongside network codes like U0074. In this case, the communication issue must be diagnosed and fixed first, as it may be the root cause of the fuel system code.
• Clogged Fuel Tank Vent: TSB #19-NA-277 describes a situation on chassis cab models where dirt and debris can clog the fuel tank vent, causing the tank to collapse or deform, which in turn damages the fuel pump module and can trigger P2635.

Diagnosis Steps

1. Connect an OBD-II scanner and check for any other accompanying codes. Prioritize diagnosis of any U-codes (network) first, followed by P018B if present.
2. Note the ambient conditions (hot/cold) when the fault occurred, as this is a key diagnostic clue for this vehicle. Hot weather points to the pump; cold weather points to the sensor.
3. Use the scanner's live data function to monitor 'Low Side Fuel Pressure,' 'Fuel Tank Pressure,' and 'Fuel Pressure Sensor Voltage.' A healthy low-side sensor should show pressure fluctuating between approximately 30 and 60 PSI with the engine running.
4. If the fault occurs in hot weather (>100°F), strongly suspect the fuel pump module per TSB #17-NA-335.
5. If the fault occurs in cold weather or is paired with P018B, test the fuel pressure sensor. With a cold engine, use the scan tool to command 'Fuel System Depressurize.' Watch the low-side pressure reading. If it does not drop to or near 0 PSI as the engine stalls, the sensor is faulty per TSB #PIP5286B.
6. Inspect the wiring and connectors for the fuel pump control module (FPCM) under the truck near the spare tire and the fuel pressure sensor on the driver's side frame rail for any visible damage, corrosion, or looseness.
7. If the sensor and wiring are confirmed good, and pressure drops are observed on the scan tool that correlate with driveability issues, the in-tank fuel pump module is the most likely culprit and should be replaced with the updated part.

Parts You'll Likely Need

• Fuel Pump Module Assembly (OEM #Varies by configuration (e.g., 13512934, 13513407)) — This is the most common fix for symptoms occurring in hot weather, as recommended by GM TSB #17-NA-335. The assembly includes the pump, sending unit, and housing. TSB #PIP5411F provides a list of updated part numbers based on wheelbase and cab size.
  Trusted brands: ACDelco (GM OE), Delphi
  OEM price range: $400-$760
  Aftermarket price range: $250-$450
• Low-Pressure Fuel Pressure Sensor (OEM #13516496 (supersedes 13579380)) — A common cause for this code, particularly when it appears in very cold weather or is paired with P018B. It's a much cheaper and easier part to replace than the fuel pump, so it should be ruled out first.
  Trusted brands: ACDelco (GM OE), Bosch
  OEM price range: $60-$80
  Aftermarket price range: $40-$60

Related Codes That Often Appear With This One

• P018B — Fuel Pressure Sensor 'B' Circuit Range/Performance. This code is frequently set with P2635, as both relate to implausible readings from the low-pressure fuel system. Nearly all relevant TSBs (#17-NA-335, #PIP5286B, #PIP5411F) explicitly link these two codes.
• P0087 — Fuel Rail/System Pressure - Too Low. This code can appear with P2635, especially in cold weather, indicating a general lack of fuel pressure reaching the engine.
• U0074 — Control Module Communication Bus 'B' Off. As noted in TSB #PIP5427B, a communication issue can sometimes trigger the P2635 code. The U-code should be diagnosed first.

Technical Service Bulletins (TSBs) & Recalls

• 17-NA-335: Supersedes earlier bulletins, confirms vapor buildup in hot weather as the cause, and recommends replacing the fuel pump module with an updated version.
• 18NA103: Addresses cold weather start/stall issues and lists P2635.
• PIP5286B: Links P2635 and P018B to a fuel pressure sensor issue and provides a specific diagnostic test.
• PIP5427B: Notes P2635 can appear with network codes like U0074.
• PIP5411F: (Superseded) Identified the in-tank fuel pump module as the cause for P2635 in high ambient temperatures.
• PIP5507B: Also describes the high-temperature stalling issue and, in cases where an updated pump is already installed, suggests using higher octane fuel.

Platform-Specific Known Issues

• High Temperature Stalling (Vapor Lock): Per TSB #17-NA-335 (which supersedes #PIP5411F and #PIP5507B), these trucks are prone to stalling or hesitation in ambient temperatures over 100°F due to vapor buildup in the fuel feed line that the original pump can't handle. The official fix is an updated fuel pump module.
• Cold Temperature No-Start/Sensor Fault: TSB #18NA103 documents issues below 20°F where the truck may start and stall or not start at all, setting P2635. This is often related to the fuel pressure sensor's performance in the cold, as detailed in TSB #PIP5286B.

Mechanic-Grade Diagnostic Values

• Low-Side Fuel Pressure (Engine Running at Idle) — expected: Fluctuating between 30 and 60 PSI. Failure: Pressure is stuck at a specific value (e.g., 48.7 PSI) and does not change, or drops significantly during hesitation.
• Low-Side Fuel Pressure Sensor Signal Voltage (Key On, Engine Off) — expected: Between 0.5V and 4.5V, depending on residual pressure.. Failure: Voltage is stuck at a specific value (e.g., 4.8V) and does not change, or reads 0V or 5V constantly.
• FPCM Power Supply Voltage (at FPCM connector) — expected: 12.0 - 12.6V (Battery Voltage). Failure: Voltage below 11.5V suggests a wiring or power supply issue before the module.
• FPCM Connector Pin 32 (Red/White wire) to Ground — expected: Battery Voltage. Failure: Low or no voltage indicates a problem with the power feed from the fuse box.
• FPCM Connector Pin 1 (Black wire) to Power — expected: Battery Voltage (testing the ground). Failure: Low or no voltage indicates a poor ground connection for the FPCM.

Scan Tool Commands That Help

• GDS2 (GM Dealer Tool): Fuel System Depressurize — Per TSB #PIP5286B, this command is used with a cold engine to test the low-pressure fuel sensor. If the pressure PID does not drop to zero as the engine stalls, the sensor is faulty.
• GDS2 (or compatible advanced scanner): Fuel Pump Enable / On — With the engine off (ignition on), this command activates the in-tank fuel pump to pressurize the low-side system. This allows a technician to check if the pump runs and if the sensor reading increases to the target pressure (approx. 60 PSI), helping to isolate a non-responsive pump or sensor.
• GDS2 (GM Dealer Tool): Fuel Pump Driver Control Module Configuration — This function may be required after replacing the Fuel Pump Control Module (FPCM) to ensure the new module is learned by the vehicle's other computers. Some service information notes this function may be missing in GDS2 and requires manually building the vehicle to access it.

Wiring & Ground Locations

• Fuel Pump Control Module (FPCM) — On the driver's side frame rail, typically above or near the spare tire.. This module controls the in-tank fuel pump. Its exposed location makes its connector susceptible to corrosion from road salt and moisture, which can interrupt power or communication, causing P2635.
• Low-Pressure Fuel Pressure Sensor — On the driver's side frame rail, in the fuel line between the fuel tank and the engine.. This sensor provides the pressure reading that the FPCM and ECM use to verify pump performance. A faulty sensor or corroded connector at this location will send incorrect data, directly causing codes P2635 and P018B.
• FPCM Connector — At the Fuel Pump Control Module on the frame rail.. Key pins for testing are Pin 32 (Red/White) for power from the fuse box, Pin 1 (Black) for ground, and the Pink and Gray wires which supply voltage to the fuel pump itself.

Real Owner Repair Stories

• YouTube channel 'mechanicRHP' (2017 Chevrolet Silverado 4.3L V6) — Check Engine Light with codes P2635 and P018B.
  ❌ Tried (didn't work) The owner noted that many online sources suggested replacing the fuel pump first, which is an expensive and difficult job.
  ✅ What actually fixed it The low-pressure fuel pressure sensor was faulty. A scan tool showed the fuel pressure reading was stuck at 48.7 PSI and would not change. Replacing the sensor, which took only a few minutes, resolved the codes.
• YouTube channel 'All Things Mechanical' (2018 Chevrolet Silverado) — Intermittent P2635 code, especially when accelerating onto the highway. Extended crank times and sluggish performance.
  ❌ Tried (didn't work) Initially, the dealership replaced the Active Grille Shutter assembly, believing a binding shutter was triggering the code. The code returned shortly after.
  ✅ What actually fixed it The dealership ultimately replaced the in-tank fuel pump assembly in addition to the active grille shutter assembly. After both parts were replaced, the P2635 code did not return. The owner concluded the fuel pump was the primary cause of the performance symptoms.

OEM Part Supersession History

• 13579380 → 13516496 — Updated design for the Low-Pressure Fuel Pressure Sensor.
• Varies (Old Design Fuel Pump) → 13512934 (Short WB Utilities), 13513407 (Short Box Crew Cab), 13513408 (Std Box Reg Cab), 13510918 (Std Box Crew Cab), etc. — Updated design to prevent vapor buildup in high temperatures, as specified in TSBs. The new design has an improved one-way breather valve.
  Heads up: It is critical to use the Electronic Parts Catalog to select the correct updated part number based on the vehicle's specific wheelbase and cab/box configuration.