P011A The two engine coolant temperature sensors disagree with each other

Engine coolant temperature sensor 1/2 correlation

Monitor

On its own the code is an engine-management fault, but on 2013-2016 Mazda CX-5 Mazda links it to a restricted heater core with overheating, so watch the temperature gauge.

It gets more serious if:

  • Inspect soon: Get it inspected soon if the engine overheats or the heater blows cold, since Mazda links P011A on the CX-5 to a restricted heater core with those symptoms.

Source: how we rate severity

P011A in short

P011A means the two engine coolant temperature sensors disagree. On the Mazda CX-5, Mazda ties it to a restricted heater core, overheating or no heat, or to software that is too sensitive in cold weather. A defective sensor or wiring can also cause it, so test before replacing parts.

Some engines have two coolant temperature sensors. The computer compares them and sets P011A when they stop agreeing within a set limit.

Mazda has the most information on this code. On 2013-2016 CX-5, Mazda says to compare the heater with another CX-5 and check heater core flow if the code comes with overheating or no heat. A separate Mazda bulletin says block heaters in freezing weather can trigger it through the computer logic, which Mazda changed.

Owner reports show the code returning after sensors are replaced, which is why TroubleCodes.net says to test each sensor before swapping it. GM diesel vans and trucks with two sensors also have a bulletin that names this code.

Most likely causes

  1. Restricted heater core or coolant flow (Mazda CX-5, Mazda6, Mazda3)

    Supported by vehicle data
    Why it ranks here
    Mazda SA218 and bulletin 07-007-19-3638 tie P011A with overheating or poor heat to a restricted heater core, and one CX-5 owner was quoted a heater core replacement. The bulletins are unverified NHTSA summaries.
    What would change this
    Rises if the heater blows cold or lukewarm while the engine is hot. Falls if cabin heat is normal.

  2. Computer error-detection logic with a block heater in freezing weather (Mazda)

    Supported by vehicle data
    Why it ranks here
    Mazda bulletin 01-015-15-3064A says P011A or P0116 can set when starting in cold weather below 32 F with a block heater, and that the control logic was changed.
    What would change this
    Rises if a block heater is used and the code appears on cold starts. Falls if no block heater is used or the weather is mild.
    How to test the engine control module (ecm / pcm)

  3. Faulty coolant temperature sensor or its wiring

    Common general cause
    Why it ranks here
    TroubleCodes.net lists a defective sensor, circuit faults and poor connections, but also warns that a good sensor may be replaced needlessly; a CX-5 owner reports the code returning after sensors were replaced.
    What would change this
    Rises if one sensor reads wrong against real temperature or a connector is damaged. Falls if both sensors track each other.
    How to test the engine coolant temperature (ect) sensor

  4. Air or coolant condition after a coolant service

    Possible — needs testing
    Why it ranks here
    A 2016 CX-5 owner reports P011A returning right after a coolant flush; this is one report.
    What would change this
    Rises if the code appears right after a coolant change or refill. Falls if the code predates any service.

What to test first

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

  1. Read all stored codes and compare both coolant temperatures on a scan tool as the engine warms up. Note other codes such as P0116.

    Low riskTool: OBD-II scan tool with live data

    • IfThe two readings drift apart

      It meansOne sensor or its circuit is suspect.

      Go to step 3

    • IfThe readings match and the code appears with overheating or poor heat

      It meansCheck heater core flow.

      Go to step 2

  2. Check whether the heater output is weak. On a CX-5, compare it with another CX-5 if possible, and have a shop check the heater core flow.

    Use caution

    Warning:Do not open the cooling system when hot. Pressurised coolant can cause burns.

  3. Have both sensors and their wiring tested individually before replacing either one.

    Best left to a shopTool: multimeter or scan tool

    Warning:This needs specialist tools and vehicle service information. Leave it to a shop.

Symptoms

  • Check engine light on
  • Poor cabin heat after warm-up
  • Engine temperature warning or overheating Gets more serious: stop and have it checked.

How to fix

  1. Check the coolant level only when the engine is cold.

  2. If you use a block heater, tell the dealer, since Mazda has a bulletin on it.

Parts and cost context

  • Engine coolant temperature (ECT) sensor:Replacing a sensor is cheap but may not fix the code if heater core flow or software is the cause. Test first; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Mazda

  • 2013–2016 · CX-5

    Supported by vehicle data

    Mazda SA218 links P011A with overheating or no heat to a restricted heater core; owners report $600 sensor jobs that did not cure it and a $1,768 heater core quote. Whether the bulletin is still current is not verified.

  • 2014–2016 · Mazda6

    Supported by vehicle data

    Mazda bulletin 01-015-15-3064A links block heater cold starts to P0116 or P011A on the Mazda6. Whether the bulletin is still current is not verified.

  • 2012–2016 · Mazda3

    Supported by vehicle data

    Mazda bulletin 01-015-15-3064A links block heater cold starts to P0116 or P011A on the Mazda3. Whether the bulletin is still current is not verified.

  • SA218Status unverified

    P011A with overheating or no heat

    2013–2016cx-5 · NHTSA 10185958

    Compare heater output with another CX-5; if the heater core flow is restricted, drain and replace coolant and replace the heater core. If P011A is set alone, follow the workshop manual.

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

  • 01-015-15-3064AStatus unverified

    Block heater cold starts set P0116 or P011A

    2012–2016mazda3, mazda6, cx-5 · NHTSA 10101466

    The computer error-detection logic can set the code below freezing with a block heater; the control logic was changed.

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

  • 07-007-19-3638Status unverified

    Poor heater performance from a plugged heater core

    2013–2019cx-5, mazda3, cx-3, mx-5 · NHTSA 10168072

    Poor heater output after warm-up from a plugged heater core; Mazda changed the coolant concentration in production, and the check engine light may come on with P011A (the summary names Mazda6 and CX-5).

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

GMC

  • 2007–2008 · Savana

    Supported by vehicle data

    GM PIP-4660 lists P011A with P2184 and P2185 on diesel vans, which have two coolant sensors. Whether the bulletin is still current is not verified.

  • PIP-4660 (Gmc)Status unverified

    Diesel coolant sensor codes P011A, P2184 and P2185

    2007–2008savana · NHTSA 10032888

    Diesels have two coolant sensors; the SES light may come on with these codes.

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

Chevrolet

  • 2007–2008 · Express

    Supported by vehicle data

    GM PIP-4660 lists P011A with P2184 and P2185 on diesel vans, which have two coolant sensors. Whether the bulletin is still current is not verified.

  • PIP-4660Status unverified

    Diesel coolant sensor codes P011A, P2184 and P2185

    2007–2008express · NHTSA 10032888

    Diesels have two coolant sensors; the SES light may come on with these codes.

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

  • P111AOn Mazda, the engine coolant temperature has gone above its limit

    Same system Possible — needs testing

    P111A is the Mazda coolant-too-hot code, while P011A compares the two coolant sensors; both appear in Mazda coolant bulletins.

All Engine cooling (thermostat) codes

P011A questions

Should I replace the coolant sensors for P011A?

Not first. A CX-5 owner replaced sensors and the code came back. Mazda ties the code to heater core flow and software on some models, so test first.

Sources and review

  1. Mazda SA218 (NHTSA 10185958): 2013-2016 CX-5 with P011A, overheating or no heat — Mazda Motor Corporation
  2. Mazda 07-007-19-3638 (NHTSA 10168072): poor heater performance from a plugged heater core with P011A — Mazda Motor Corporation
  3. Mazda 01-015-15-3064A (NHTSA 10101466): block heater cold starts set P0116 or P011A — Mazda Motor Corporation
  4. P011A trouble code overview — TroubleCodes.net
  5. NHTSA complaint ODI 11195533: Mazda CX-5 2013, P011A coolant sensor replacement did not cure — NHTSA Office of Defects Investigation
  6. NHTSA complaint ODI 11728567: Mazda CX-5 2016, P011A after coolant flush — NHTSA Office of Defects Investigation
  7. GM PIP-4660 (NHTSA 10032888): coolant sensor DTCs P011A, P2184 and P2185 on diesel vans and trucks — General Motors
Last reviewed
Written by
Saurabh K.
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