Fix P0116: Mechanic’s solutions that WORKED

The code P0116: Engine Coolant Temperature Sensor Circuit Range/Performance Problem means that a fault has been detected in the range or performance of the engine coolant temperature sensor circuit. Most likely caused by the ECT sensor, its wiring, or possibly needs PCM update.

P0116 quick overview

Meaning	Engine Coolant Temperature Sensor Circuit Range/Performance Problem
Is it serious?	It can be, especially if it leads to incorrect engine temperature readings, which can cause poor engine performance or even damage.
Possible causes	– Faulty engine coolant temperature sensor. – Wiring or connection issues related to the temperature sensor. – In some models, an outdated Engine Control Module (ECM) software that requires a reflash. – Grounding issues, especially if other systems like cooling fans are interfering with sensor readings.
How to diagnose?	Visual Inspection: Start by checking the engine coolant temperature sensor for any visible damage or disconnections. Check Wiring: Inspect the wiring connected to the temperature sensor. Look for frayed wires, corrosion, or any disconnected plugs. Coolant Level and Condition: Ensure the coolant reservoir is filled to the appropriate level, and the coolant is in good condition. Resistance Test: Using a multimeter, test the sensor’s resistance and compare with manufacturer’s specifications (these can often be found online or in a vehicle repair manual). Inspect Grounds: Examine grounding points, especially around the engine bay, for corrosion or disconnections. Clean and secure any that appear compromised. Interference Check: Note any patterns with other systems, such as the cooling fan. For instance, if the temperature reading drops suddenly when a fan or another component activates, there may be an electrical interference or grounding issue. Check for Modifications: Ensure that there haven’t been any aftermarket modifications or previous repairs that might interfere with the sensor or its circuitry.
What is ECT sensor?	The ECT (Engine Coolant Temperature) sensor measures the temperature of the engine coolant and sends this data to the engine control module (ECM) to optimize engine performance and fuel efficiency.

How to fix P0116 – learn from mechanics

I looked into P0116 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Audi

Vehicle Information:
2005 GMC Yukon XL 2500 SLE 6.0L
MIL Lamp Issue

Issue + Repair History:

• The vehicle returned four times with the same P0116 code.
• First visit: Coolant was low due to a leaking water pump.
• Second visit: Installed a new coolant temp sensor.
• Third visit: Replaced intake air temperature sensor, which is part of the mass air flow sensor.

Suggestions from the Community:

• Check for drivability symptoms and monitor the engine temperature.
• Potential issues might involve connectors, not just sensors.
• Inspect the thermostat and look for any current calibration updates.
• The code might indicate the engine isn’t warming up quickly enough; replacing the thermostat was suggested.
• Start from cold and monitor how long it takes the engine to reach operating temperature. If it takes too long, replace the thermostat.
• Consider if the customer is using a block heater, which might cause the code.
• Check for potential PCM updates, or issues with the coolant sensor or its connector.

Final Fix:
The problem was traced to the connection on the temperature sensor. The connection intermittently failed to make contact, causing the temperature reading to drop to -40°F. A new connector was installed, resolving the issue.

Case #2: Saab

Vehicle Information:
1999 Saab 9-5 SE 2.3L
Stall Issue When Put in Reverse

Issue + Repair History:

• The engine stalled when cold and placed in reverse.
• MIL light turned on in early December and turned off after four days, with a P0116 code indicating an ECT performance problem.
• Checked intake hoses, throttle valve, and body, all were fine.
• A jingle/rattle noise from the front of the engine was also reported, but the origin couldn’t be determined.

Suggestions from the Community:

• Be cautious about the rattle noise in the front, as it could indicate damage from the harmonic balancer breaking apart.
• The P0116 code usually indicates a faulty thermostat, which is often misdiagnosed as a sensor issue.
• Check the thermostat’s performance, specifically if it opens at 190°F.
• Replace the ECT (Engine Coolant Temperature) sensor as it’s an inexpensive part.

Final Fix:
The stalling issue was due to a vacuum check valve between the throttle body and PCV at the valve cover. The port broke off, causing a vacuum leak, which was fixed with a replacement part (Saab #43 01 669). To address the P0116 code, both the thermostat and temperature sensor were replaced.

Case #3: Volvo

Vehicle Information:
1997 Volvo 850 GLT 2.4L
MIL Lamp Illuminated, Cooling Fans Constantly On

Issue + Repair History:

• The vehicle arrived with the MIL light on, and code P0116 (equivalent to Volvo’s DTC 123) related to the ECT sensor was found.
• The ECT sensor was found to have an intermittent open and was replaced.
• The issue returned two days later.
• Further testing for reference signal and/or sensor ground did not reveal any abnormalities.
• A Technical Service Bulletin (TSB) suggested that a false code might be related to the ECU. The ECU was replaced, but the problem returned after two days.

Suggestions from the Community:

• The thermostat might not be functioning correctly, which can trigger a code 123, typically pointing to either a faulty ECT sensor or a bad thermostat.
• Another Volvo model had a similar ECT code issue that was resolved by addressing a corroded ground wire under the right front headlight.
• If the ECU detects too long of a warm-up cycle with the ECT, it might set this code. Thermostats known to stick open can cause this problem.
• Ensure ECT connector pins are clean and tight; a prior case had issues with these connectors causing the cooling fan to run incessantly.
• Bad grounds can set this code during startup. Check ground readings when the starter is engaged.
• Most code 123 cases are due to bad thermostats, often found cracked or stuck slightly open.

Final Fix:
After removing the thermostat, it was found to be broken. This was the root cause of the problem, and after its replacement, the issue was resolved.

Case #4: Nissan

Vehicle Information:
2008 Nissan Maxima SE 3.5L

Issue + Repair History:

• The vehicle displayed code P0116.
• No external coolant leaks were observed.
• The coolant reservoir was nearly empty, yet the vehicle had never overheated, and the temperature gauge was working normally.

Suggestions from the Community:

• There’s a Technical Service Bulletin (TSB) named NTB08-030, which suggests the PCM (Powertrain Control Module) might need reprogramming. Check the PCM part number to ensure the TSB applies.
• Another suggestion recalled a TSB related to an ECT sensor code where the fix was an ECM reflash, which needs to be confirmed for this vehicle.
• The vehicle might need an ECM reflash, requiring a dealer visit, especially if the technician does not have the required ‘consult 3’ equipment.
• Another Service Bulletin, SB-09-090, addresses the P0116 code, with a National Traffic Highway Safety Administration (NTHSA) item number #10030712. It’s recommended to verify if this is covered by Nissan’s extended powertrain warranty before proceeding with repairs.
• Classification EC08-004, Reference NTB08-030 dated March 6, 2008, specifically mentions the 2008 Maxima with the P0116 code. If the DTC P0116 is stored in the ECM and there are no other drivability symptoms, verify if the current ECM part number matches those listed in the bulletin. If it matches, the ECM needs reprogramming.

Final Fix:
After consulting the TSB, it was confirmed that the ECM required a reflash to address the P0116 code. The cooling system was found to be normal.

Case #5: BMW

Vehicle Information:
2011 BMW 328i xDrive 3.0L

Issue + Repair History:

• The car arrived at the shop with the MIL (Malfunction Indicator Lamp) activated.
• Upon inspection, the temperature sensor was found to be reading 20°F, despite the car sitting in a shop where the ambient temperature, oil, and coolant leaving the radiator were all around 65°F.
• The temperature sensor was replaced, which seemed to rectify the temperature reading issue.
• The cooling system was flushed, and a bleed procedure was performed with a scanner, and everything appeared normal.
• After a brief drive, the MIL light came back on. The same codes were present, and when graphing the coolant sensor data, it was observed that the temperature sensor reading would drop to -54°F every time the electric cooling fan was activated. When the fan was switched off, the temperature reading returned to normal.

Suggestions from the Community:

• Inspect the wiring because even a new part could be faulty.
• Verify that the replaced sensor was of OEM (Original Equipment Manufacturer) quality and check the wiring.
• The third suggestion pointed to a potential bad ground as the culprit, as the temperature sensor circuit might be receiving feedback from the fan circuit due to a poor ground.

Final Fix:
The ground was identified as the problem. The wiring to and from the sensor was in good condition, but after cleaning some grounds and adding a ground wire to the cooling fan, the problem was resolved.