How To Test: P0116 OBD II Trouble Code (Honda 2.2L, 2.3L)

OBD II trouble code P0116 ECT Sensor Range/Performance Problem usually points to one of several things: a bad thermostat (one that's stuck open), or an overheating problem, or a bad engine coolant temperature (ECT) sensor (although its rare for a failed ECT sensor to set this code).

Thankfully, there is a way to find out what's going. In this tutorial, I'm gonna' go into the specifics of why your Honda sets a P0116 trouble code and, more importantly, I'm going to show you how to troubleshoot this diagnostic trouble code (DTC) in a step-by-step way.

P0116 Basics You Need To Know

The optimal operating temperature range of your Honda's engine, as measured by the engine coolant temp (ECT) sensor, is around 176 to 200°F (80 to 93°C).

At this temperature range, your Honda Accord is running at its most efficient level to control/reduce emissions and give the best gas mileage possible (as long as there are no other faults present of course).

To explain this a bit further, the colder the engine is, the more fuel the fuel injection computer (known as the PCM = Powertrain Control Module) needs to inject. The warmer the engine is, the less fuel the PCM is needs to inject.

Your Honda's PCM uses the engine coolant temperature (ECT) sensor to ‘sense’ the engine's operating temperature and thus inject more or less fuel, control ignition timing advance, and a few other things.

Now, when a code P0116 ECT Sensor Range/Performance Problem lights up the check engine light (CEL) on your Honda's instrument cluster, the PCM is letting you know that the engine hasn't reached or has overshot the normal operating temperature range (176 to 200°F (80 to 93°C)).

NOTE: The coolant temperature may go up as high as 225 to 227°F (107 to 108°C) before the engine cooling fan comes on and this is normal. The temperature should drop down to about 200°F (93°C) before the fan stops and the cycle repeats itself.

How The ECT Sensor Works

Although a P0116 ECT Sensor Range/Performance Problem doesn't necessarily accuse the engine coolant temperature (ECT) sensor as bad... it does help to know how the ECT sensor operates and reports the engine's coolant temperature.

Briefly, this is how the engine coolant temperature (ECT) sensor works:

1. The engine coolant temperature (ECT) sensor is a 2 wire sensor.
   1. One wire (circuit) supplies power.
      • Power is in the form of 5 Volts DC and is provided only with Key On Engine Off (KOEO) or Key On Engine Running (KOER).
      • Power is provided by the PCM.
   2. The other wire (circuit) supplies Ground.
      • This Ground is fed to the ECT sensor by the PCM (internally).
2. The ECT sensor is a resistor (thermistor). Its resistance changes in response to changes in the air's temperature.
   • The cooler the engine coolant, the higher the resistance of the ECT sensor.
   • The warmer the engine coolant, the lower the resistance of the ECT sensor.
3. When the 5 Volts pass through the engine coolant temperature (ECT) sensor, the resistance of the sensor produces a voltage drop. This in plain English means that only a certain amount of the 5 Volts are let through to the Ground wire.
   1. The cooler the engine coolant is, the less voltage is let thru' onto the Ground wire (due to the ECT sensor's higher resistance).
      • The PCM translates this higher voltage drop into a colder temperature value.
   2. The warmer the engine coolant, the more Voltage is let thru' onto the Ground wire (due to the ECT sensor's lower resistance).
      • The PCM translates this lower voltage drop into a warmer/hotter temperature value.

With this bit of information, let's move on to the next subheading.

Symptoms Of A P0116 Diagnostic Trouble Code

When the PCM senses that your Honda's engine doesn't reach normal operating temperature, your Honda isn't gonna' run/perform optimally.

You may see one or more of the following symptoms when the engine coolant temperature (ECT) sensor fails:

1. Check engine light (CEL) is on.
2. DTC P0116 is present.
3. Won't pass the state mandated emissions test.
4. Gas mileage will suffer.
5. Temperature gauge's needle show's a cold engine no matter how long the engine's running.
6. Heater blows only cold air (winter time).
7. Engine is overheating.
8. Hard start and/or extended cranking time (after shut off).
9. Black smoke coming out of the tailpipe.

Let's find out what are the common causes of a P0116 DTC, in the next subheading.

Common Causes Of A P0116 Trouble Code

The most common cause of trouble code P0116 is the engine not being able to reach normal operating temperature due to a bad thermostat. Specifically, one that's stuck open or has been removed.

The other most commonly reported cause of code P0116 is a very low level of coolant in the coolant system.

Here's a more complete list:

1. Engine doesn't reach normal operating temperature:
   • Defective thermostat (that's stuck open).
   • Fan motor that's been wired ‘direct’ and is on all of the time the engine is running.
   • Bad engine coolant temperature sensor (it is extremely rare).
2. Engine is overheating:
   • Bad thermostat (one that's stuck closed).
   • Bad fan motor(s).
   • No coolant in cooling system.
   • Blown head gasket.

With this basic info under our belts, let's turn the page and get testing!