Back to 2021 Honda Civic
Help
2021 HONDA CIVIC
1.5L I4 Turbo•FWD•CVT•gas•turbo
4 active safety recalls on this vehicle — view recalls
Founding sponsor spot is openYour name on every procedure for this vehicle, permanently.Sponsor — $99 →
Repairs403Labor504Torque3392Fluid7DTC1173Battery1Maintenance0Recalls4
P1486moderate severityPowertrain

Thermostat Range/Performance Problem

on 2021 Honda Civic 1.5L I4 Turbo · FWD

What this code means

The engine coolant isn't reaching or holding the expected temperature, pointing to a thermostat issue. Similar to OBD generic P0128.

Symptoms

  • Check engine light on
  • Slow engine warm-up
  • Poor heater output

Common causes

  • Stuck-open thermostat
  • Faulty coolant temp sensor
  • Low coolant level
  • Cooling system fault

Diagnostic steps

  1. Scan and confirm P1486
  2. Monitor coolant temp during warm-up
  3. Inspect thermostat operation
  4. Verify coolant temp sensor readings
🔌 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 →
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Mechanic · 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 2021 Honda Civic 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 Honda Civic — $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 →