Powertrain, generic · Fuel and air metering

P011A Engine Coolant Temperature Sensor 1/2 Correlation

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Some engines have two coolant temperature sensors that check each other. P011A is set when both are electrically fine but their readings differ more than a calibrated amount under conditions where they should agree. Mazda documents the code for the 2013–2016 CX-5 and 2014–2016 Mazda6: sensor 2 sits in the heater hose, and a clogged heater core keeps it noticeably colder, so P011A often comes with weak cabin heat although both sensors are good. Mazda's check is to compare both sensors with ambient temperature after an overnight soak and then the temperature difference across the heater hoses. A block heater used below 0 °C can also trigger it.

Likely causes

Clogged heater core or restricted coolant flow at sensor 2
One of the two sensors drifting
Air in the cooling system or low coolant level
Block heater use in frost
Contact resistance at one sensor

Symptoms

  • Check engine light on
  • Weak cabin heating (typical on Mazda)
  • Otherwise often no driving symptoms

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,200
Time0.5–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

engine coolant temperature sensorengine coolant temperature sensor 2heater core

Related codes

P0116P2183P011BP011EP011FP0128

References: law.cornell.edu, static.nhtsa.gov, hella.com.