START HERE: Troubleshooting DTC P0117
As mentioned in the previous page, the reason your Honda's fuel injection computer is registering a P0117 ECT Sensor Circuit Low Voltage OBD II diagnostic trouble code (DTC) is that it thinks that the engine coolant temperature is around 300°F (150°C) or higher.
Fortunately, testing the engine coolant temperature (ECT) sensor is not hard and it's something that you can do yourself with a scan tool with Live Data capability.
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.
Here's a brief description of the tests you'll be doing with the help of this tutorial:
- Confirm the ECT sensor's temperature value.
- The first thing we need to do is to see what temperature the ECT sensor is reporting.
- What we're looking for is to see if the ECT sensor is reporting a temp that's 300°F (150°C) or higher.
- TEST 1: Checking The Engine Coolant Temperature Value.
- Check that the ECT sensor connector's wiring is not shorted together.
- 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 The Condition Of The ECT Sensor's 2 Wires.
- Unplugging the ECT sensor and verifying the PCM sees an extreme cold temperature.
- In this test step, we'll unplug the ECT sensor from its connector and then, via the scan tool's Live Data mode, see if the PCM now reads -4 °F (-20 °C).
- This test will help you to eliminate a bad PCM and/or a hidden electrical short somewhere in the wiring between the PCM and ECT sensor.
- TEST 3: Disconnecting The ECT Sensor From Its Connector.
TEST 1: Checking The Engine Coolant Temperature Value
By now I'm sure you're tired of hearing this but I'll say it again: when your Honda's PCM registers a trouble code P0117 ECT Sensor Circuit Low Voltage, it's seeing an engine coolant temperature of 300°F (150°C) or higher.
So the first thing we'll do is confirm this extreme hot temperature using a scan tool's engine coolant temperature (ECT) sensor's PID input.
On your scan tool the ECT sensor's PID (Parameter Identification) is labeled as: COOLANT. This is the PID that will let us see the engine coolant temp that your Honda's PCM is seeing (see the photo in the image viewer on the left of this paragraph).
If you don't have a scan tool and you need to buy one, check out my Actron CP9580 Scan Tool Review.
IMPORTANT: This test section assumes that you're starting out with a completely cold engine. Starting the test with a completely cold engine will ensure the accuracy of your test results.
OK, this is what you need to do:
Connect your scan tool to your Honda (or Acura) car or mini-van and turn the key to the on position.
NOTE: This test is done with the Key On Engine OFF (KOEO).
Go to its Live Data mode once the scan tool has powered up.
Scroll down to the PID labeled COOLANT (°F)
The COOLANT PID should register a temperature that's ±10 °F of ambient temperature (if all is normal)
- So let's say that it's 50 °F outside, then the ECT sensor PID should register something between 40 to 60 °F.
You'll see one of three possible temperature results:
- -4°F (-20°C).
- 300°F (-150°C).
- The current outside coolant temperaute.
Let's interpret your test results:
CASE 1: Your scan tool shows a 300 °F reading. This confirms that there is a problem with the engine coolant temperature (ECT) sensor.
This test result also confirms that the code P0117 ECT Sensor Circuit Low Voltage Input, that was stored in the PCM's memory is telling you the truth.
The most likely cause will be that the ECT sensor circuits (wires) are shorted together. This usually happens in the section of the 2 wires nearest to the ECT sensor's connector.
The next step is to physically check the condition of the wires and do a simple wiggle test. Go to: TEST 2: Checking The Condition Of The ECT Sensor's 2 Wires.
CASE 2: Your scan tool shows a -4 °F (-20°C) reading. This confirms that you do have a problem with the engine coolant temperature (ECT) sensor or its circuits.
Seeing an extreme cold temperature of -4 °F (-20°C) indicates one of two things, either that the ECT sensor is bad or the ECT sensor connector's wires have an open-circuit problem (think unplugged sensor). You'll also see a diagnostic trouble code P0113 (ECT Sensor Circuit High Voltage) stored in the PCM's memory.
CASE 3: Your scan tool shows a temperature reading that's ±10 °F of ambient temperature- This tells you that at the moment the ECT sensor and its circuits are OK and more importantly, that the problem is intermittent.
But, since your scan tool retrieved a DTC P0117 the problem may just be hiding at the moment, I recommend clearing the diagnostic trouble code (DTC) and road testing your vehicle to see if the code comes back.
If the P0117 DTC does come back, repeat this test once more.