P26A3 Engine coolant bypass valve A range or performance problem

Coolant bypass valve performance

P26A3 in short

P26A3 means the engine computer saw the coolant bypass valve, which steers coolant around the engine, not reaching the position or temperature effect it commanded. Check the coolant level and look for leaks first, then have the valve tested and bulletins checked. Get it inspected soon, and stop if the engine overheats.

The coolant bypass valve (Subaru calls it a thermo control valve, Honda an electric water valve) is an electrically driven valve that controls where coolant flows during warm-up and driving.

The engine computer compares the valve's commanded position with coolant temperature, radiator outlet temperature and how fast the engine warms up. P26A3 sets when those do not agree, which usually means the valve is sticking, broken inside or not responding.

Several makers have bulletins: Ram for a broken internal gear and for contaminated coolant, Honda for software on plug-in hybrids, and Subaru for a revised thermo control valve. On some Subaru models, EyeSight is switched off while the code is set.

Most likely causes

  1. Sticking or internally broken bypass valve

    Supported by vehicle data
    Why it ranks here
    The code compares commanded and actual valve behaviour, so a valve that sticks or breaks inside is the direct cause. FCA replaces the valve for a broken internal gear, and owners of Subaru and Nissan models report the valve replaced for this code.
    What would change this
    Rises if the valve does not respond to a scan-tool command or P26A6/P2681 also set; falls if the valve moves correctly.

  2. Contaminated coolant jamming the valve (2023-2024 Ram 1500)

    Supported by vehicle data
    Why it ranks here
    FCA's bulletin for P26A3 on 2023-2024 Ram 1500 trucks flushes the cooling system as well as replacing the valve, because contamination affects the new valve too.
    What would change this
    Rises if the coolant is discoloured, has debris or the wrong type has been mixed in.

  3. Low coolant or a leak

    Possible — needs testing
    Why it ranks here
    With low coolant, the temperatures the computer reads no longer match what the valve should be producing. Low coolant is listed as a cause of bypass valve codes.
    What would change this
    Rises if the level is low when cold or there are signs of a leak.

  4. Engine computer software (Honda plug-in hybrids)

    Supported by vehicle data
    Why it ranks here
    Honda's bulletins for the 2018 Clarity Plug-in Hybrid and 2014 Accord Plug-in Hybrid address P26A3 (electric water valve malfunction); the Clarity bulletin is a PCM software fix.
    What would change this
    Rises if a bulletin covers your vehicle and the update has not been done.
    How to test the engine control module (ecm / pcm)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. With the engine fully cold, check the coolant level and look around the bypass valve and its hoses for wet spots, dried coolant crust or a sweet smell.

    Low riskTool: flashlight

  2. Have a shop check for bulletins, then command the valve through its range with a scan tool and compare its position and the coolant temperatures with the service information.

    Best left to a shopTool: scan tool with active tests, service information

    Warning:The test needs the engine running and warm, near hot coolant and moving parts. Leave this to a shop.

Symptoms

  • Check engine light
  • EyeSight or other driver-assist features disabled (Subaru)
  • Slow warm-up or weak heater
  • Temperature gauge rising or overheating warning Gets more serious: stop and have it checked.
  • Loss of power or stalling Gets more serious: stop and have it checked.

How to fix

  1. Write down every stored code and the freeze-frame data before clearing anything.

  2. With the engine fully cold, check the coolant level in the reservoir and top up with the coolant type the owner's manual specifies if it is low; a level that keeps dropping means a leak to find.

    Warning:Never open the radiator cap or pressurised reservoir while the engine is hot.

  3. Ask a dealer whether a bulletin or support program covers your vehicle before paying for a valve; several makers have them for this code.

On your vehicle

Ram

  • 2022–2024 · 1500

    Supported by vehicle data

    FCA has two bulletins for P26A3: a broken internal valve gear (2022-2023) and contaminated coolant needing a flush and a new valve (2023-2024).

  • 07-005-24Status unverified

    FCA 07-005-24: broken internal coolant valve gear

    2022–20231500 · issued · NHTSA 11001237

    With P26A3, P26A6 or P2681 set, the 3-way coolant valve is replaced because of a broken internal gear.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 07-007-24Status unverified

    FCA 07-007-24: coolant contamination with P26A3

    2023–20241500 · issued · NHTSA 11006531

    With P26A3 set, the cooling system is flushed and the three-way coolant valve replaced.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Subaru

  • 2019–2021 · Forester

    Supported by vehicle data

    Owners report P26A3 traced to the thermo control valve, with EyeSight switched off until it is fixed. Subaru released a new valve under bulletin 09-80-21, though the bulletin summary does not name the code.

  • 09-80-21Status unverified

    Subaru 09-80-21: new thermo control valve assembly

    2019–2021forester, outback, legacy, crosstrek · issued · NHTSA 10208664

    Announces a revised thermo control valve for 2019-2021 Forester, 2020-2021 Legacy and Outback and 2021 Crosstrek. NHTSA's summary does not name P26A3; owners connect the two.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Honda

  • A18-090Status unverified

    Honda A18-090: PCM software, P26A3 electric water valve

    2018clarity · issued · NHTSA 10166784

    On the 2018 Clarity Plug-in Hybrid, a PCM software problem can turn on the MIL with P26A3, P100C or P0010.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • A20-033Status unverified

    Honda A20-033: MIL with P26A3 electric water valve malfunction

    2014accord · issued · NHTSA 10179389

    Applies to the 2014 Accord Plug-in Hybrid with P26A3. NHTSA's summary does not give the repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P2681Engine coolant bypass valve A control circuit open or out of range

    Same system Supported by vehicle data

    P2681 is the bypass valve's electrical circuit fault. FCA lists both codes for a broken internal valve gear on the Ram 1500.

  • P26B7Engine coolant bypass valve C control circuit open

    Same system Common general cause

    P26B7 is the circuit fault for bypass valve C on engines with more than one valve, mainly Ford.

All Engine cooling (thermostat) codes

P26A3 questions

Why did my Subaru turn off EyeSight with P26A3?

Owners report EyeSight and other driver-assist features switching off while P26A3 is set. Fixing the valve fault and clearing the code is what restores them; ask the dealer about bulletin 09-80-21.

Sources and review

  1. TAT Scandata: P26A3 Engine Coolant Bypass Valve 'A' Range/Performance — Technical Assistance Team (TAT), Australia
  2. FCA 07-005-24: Broken internal coolant valve gear, P26A3/P26A6/P2681 — FCA US / NHTSA ,
  3. NHTSA complaint ODI 11518902: 2019 Subaru Forester, P26A3 thermal control valve, EyeSight disabled — NHTSA Office of Defects Investigation (complaint flat file) ,
  4. NHTSA complaint ODI 11629519: 2023 Nissan Rogue, P26A3-00, bypass valve replaced, stall — NHTSA Office of Defects Investigation (complaint flat file) ,
  5. 2023 Integra Owner's Manual: How to Handle Overheating — American Honda Motor Co.
  6. Toyota Camry Owner's Manual (OM06291U, 2.5L A25A-FKS / 3.5L 2GR-FKS) — Toyota
  7. 2019 Ranger Workshop Manual 303-03 Engine Cooling 2.3L EcoBoost: Description and Operation (Fail Safe Cooling) — Ford Motor Company
  8. NHTSA complaint ODI 11474804: 2020 Subaru Forester, P26A3 thermo control valve, safety features disabled — NHTSA Office of Defects Investigation (complaint flat file) ,
  9. FCA 07-007-24: Coolant contamination, P26A3, cooling system flush — FCA US / NHTSA ,
  10. P26B7: Coolant Bypass Valve C Control Circuit/Open — Kelley Blue Book
  11. Honda A18-090: PCM software, P26A3 electric water valve — American Honda Motor Co. / NHTSA ,
  12. Honda A20-033: MIL with P26A3 electric water valve malfunction — American Honda Motor Co. / NHTSA ,
  13. Subaru TSB 09-80-21: new thermo control valve assembly (bulletin page) — CarComplaints.com
Last reviewed
Written by
Saurabh K.
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