Free API
Help
2009 GMC ENVOY
4.2L I6•4WD•AUTOMATIC•gas
Founding sponsor spot is openYour name on every procedure for this vehicle, permanently.Sponsor — $99 →
Repairs0Labor985Torque4693Fluid18DTC3914Battery2Maintenance0Recalls0
P1810high severityPowertrain

TFP Valve Position Switch Circuit

on 2009 GMC Envoy 4.2L I6 · 4WD

What this code means

The PCM/TCM detected a fault in the Transmission Fluid Pressure (TFP) manual valve position switch circuit. This switch tells the TCM what gear range the driver has selected.

Symptoms

  • Check Engine Light
  • Transmission stuck in one gear
  • Incorrect gear selection display
  • Harsh shifting
  • No reverse

Common causes

  • Faulty TFP switch (internal to transmission)
  • Wiring issue to TFP switch
  • Transmission connector damage
  • TCM failure
  • Low transmission fluid affecting pressure switch

Diagnostic steps

  1. Check transmission fluid level and condition
  2. Read TFP switch data with scan tool
  3. Test TFP switch circuit resistance
  4. Inspect transmission connector
  5. Compare commanded gear to actual gear

Repair notes

Check fluid level first. TFP switch is internal to the transmission and requires pan removal to access. Replace switch or repair connector.

🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
✓ ANCEL official store
Serious DIY~$100
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
SHOP FAVORITE
Shop-grade tablet~$300
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Other Powertrain codes on this vehicle

🔌 Need this data in your app? It's all in the free API →
🔧 Built by master technician Chris Hackleman · Master Technician · 20+ years. Spot an error? Use the Help link above — a human reads every report.
Stuck on this repair? Take it to The Diag Desk — ask a master tech about this exact car → real human answer within 24h, never AI
Share:XRedditFBWhatsAppThreadsEmail
⚠ STILL BEHIND THE PAYWALL
The 2009 GMC Envoy repair data is incomplete because no one has sponsored it yet. For $99, we generate the full step-by-step procedures, then fact-check them with a second AI pass and your expert review. Your name on every procedure, permanently.
The same data would cost $169/mo from Mitchell1 or $30/year from ALLDATAdiy — and you'd be renting access, not freeing it. Sponsor once, free forever.
Sponsor the GMC Envoy — $99 →
Building an app?
Free API access to all this data — 10 requests/day, no card required.
Get an API key →
Run a shop?
Manage repairs, estimates, and customers with ShopBase — $249/mo, all features included.
Try ShopBase →