START HERE: Troubleshooting DTC P0116
The reason your Honda's fuel injection computer is registering a P0116 ECT Sensor Range/Performance Problem OBD II diagnostic trouble code (DTC) is the fact that the engine just isn't operating within normal operating engine temperatures.
Fortunately, you and I can find out if the engine is warming up sufficiently or overheating. How? you might ask. The answer is by connecting a scan tool with Live Data capability to your Honda and verifying the temperature that the ECT sensor is reporting as the thermostat opens.
Now, if you don't have a scan tool with Live Data capability and need to buy one, check out my recommendation here: Actron CP9580 Scan Tool Review.
So, to get this show on the road, let me briefly describe the 2 tests you'll be doing to troubleshoot the P0116 ECT Sensor Range/Performance Problem diagnostic trouble code (DTC) lighting up your Honda's check engine light (CEL).
Basically, you will:
- Check the operation of the thermostat.
- This test will let us know if the thermostat is stuck open or stuck closed.
- TEST 1: Checking Engine Thermostat Operation.
- Checking radiator cooling fan Operation.
- We'll check that the ECT sensor's connector is OK and not damaged (which could be causing a false contact condition).
- This involves removing the hard plastic protector that's over the wires and inspecting the condition of the two ECT sensor wires.
- We'll also do a wiggle test of the ECT sensor's 2 wires.
- TEST 2: Checking cooling fan motor Operation.
NOTE: The coolant temperature may go up as high as 225 to 227°F (107 to 108°C) before the fan or fans come on and this is normal. The temperature should drop down to about 200°F (93°C) before the fans stop and the cycle repeats itself.
TEST 1: Checking Engine Thermostat Operation
As mentioned before, when your Honda's PCM registers a trouble code P0116 ECT Sensor Range/Performance Problem, it's because the PCM is sensing that the engine is not reaching its normal operating temperature or it's overheating.
So, to get our P0116 trouble code diagnostic on its way, the first thing we'll do is test the operation of the thermostat.
You'll need a scan tool with Live Data capability. If you don't have or need to upgrade yours, take a look at my recommendation here: Actron CP9580 Scan Tool Review.
IMPORTANT: It's super important that you start this test with a cold engine. This is not only a safety measure but will ensure the accuracy of the thermostat test.
OK, this is what you need to do:
Connect your scan tool and turn the Key On Engine Off (KOEO). Then go to its Live Data mode. Once in Live Data, go to the PID labeled COOLANT (see photo 1 of 2 in the image viewer above). The PID COOLANT gets its temperature value directly from the ECT sensor.
Your scan tool should register an ECT sensor temperature of ±10°F of whatever the outside temperature is. You can also confirm this by comparing the IAT sensor's PID temperature value with the COOLANT PID value since these two will be almost identical with a completely cold engine (see photo 2 of 2 in the image viewer).
IMPORTANT: You must start with a completely cold engine for this test to work.
Open the radiator and check its coolant level. If applicable, add coolant.
At this point, with the engine completely cold (and off), touch the upper radiator hose with the palm of your hand and check its temperature. It should be cold to the touch (with ‘cold’ I mean at ambient temperature).
Start your Honda's engine and let it warm up.
Your job from this point forward is to observe the ECT sensor PID on your scan tool and check that the temperature is increasing.
Periodically, check the upper radiator hose's temperature as the engine warms up with your hand.
The upper radiator hose should be cold (no heat) to the touch up until your scan tool registers 170°F (76°C) for the ECT sensor temperature.
When the scan tool shows the COOLANT temperature at 190°F (87°C) or higher, the upper radiator hose should start getting hot to the touch.
At any temperature above 190°F (87°C), the upper radiator hose should be hot no ‘ands, ifs or buts’, since the thermostat should be fully open and letting hot coolant pass into the radiator
PRECAUTION: Lightly touch the upper radiator hose once the thermostat has opened up because the its gonna' be hot. Be careful and use common sense.
Turn off the engine if the upper radiator hose DOES NOT get hot at 190 to 195°F (87-90°C) and let the engine cool down.
If this happens in your case, then the thermostat is stuck closed. The end result is that the engine will over-heat.
NOTE: In a case like this I grab a small shop fan and I place it on the engine. I turn the fan on and let it cool the engine down.
Let's interpret your test results:
CASE 1: The upper radiator hose got warm to hot way before 190°F (87°C)- This confirms DTC P0116 and that the thermostat is stuck open or missing.
What usually happens is that within 1 or 2 minutes of the engine starting (and warming up), the upper radiator hose starts to get warm (to hot) to the touch.
This is a clear indication that the thermostat is either missing or is stuck open.
Your next step is to replace the thermostat with the factory recommended temperature range thermostat of 195°F.
CASE 2: The upper radiator hose got warm to hot at 185 to 190°F (85 to 87°C)- This confirms that the thermostat is functioning correctly.
Your next step is to test the operation of the cooling fan motors. For this test go to: TEST 2: Checking cooling fan motor Operation.
CASE 3: The upper radiator hose DID NOT get hot at 190°F (87°C) or beyond. This confirms that the thermostat is bad and is stuck closed.
This also means that the thermostat is causing your Honda's engine to over-heat. Your next step is to let the engine cool down completely and buy the thermostat.