98' Cavalier- code PO118-ECT sensor circuity high voltage

[FShutz]

I replaced the CTS (Coolant temp sensor) on my 98' Cavalier (2.2L OHV). Now once it reaches norm. oper. temp. the Ck eng light (code PO118) comes on & the fan stays on. Furthermore, the temp. guage pegs far left and stays there & wont read proper. Any suggestions ? Also replaced the egr with new. Thanks alot !

[GMCSonoma]

Did you bleed the coolant system afterwards???

Otherwise:
DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage




Circuit Description

The engine coolant temperature (ECT) sensor uses a thermistor in order to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on the signal circuit to the sensor. When the engine is cold, the sensor resistance is high, therefore, the ECT signal voltage will be high.
As the engine warms, the sensor resistance becomes less and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.
The ECT sensor controls the following items:

• The fuel delivery
• The torque converter clutch (TCC)
• The ignition control (IC)
• The evaporative emission (EVAP) canister purge valve
• The idle air control (IAC) valve
• The electric cooling fan

Conditions For Setting The DTC

• The engine run time is greater than 60 seconds.
• The ECT sensor indicates that the engine coolant temperature is less than -40°C (-40°F) for 6.25 seconds.

Action Taken When the DTC Sets

• The Malfunction Indicator Lamp (MIL) will illuminate.
• The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
• A history DTC stores.
• The coolant fan turns ON.
• The PCM will default to 20°C (68°F) for the first 60 seconds of the engine run time and then to 92°C (198°F). The scan tool may show the defaulted value.

Conditions for Clearing the MIL/DTC

• The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
• A history DTC will clear after 40 consecutive warm-up cycles without a fault.
• The MIL/DTCs can be cleared by using the scan tool.

Diagnostic Aids

• The normal operating temperature for the engine cooling system is between 90°C (194°F) and 95°C (203°F).
• Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature vs Resistance .

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

1. <LI value=1>The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
   <A name=TD04><LI value=4>This step simulates a DTC P0117. If the PCM senses the change, then the PCM and the ECT wiring are OK.
   <A name=TD11>
2. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to PCM Replacement/Programming for PCM programming and the CKP System Variation Learn Procedure for the Crankshaft Position System Variation Learn Procedure.

DTC P0118-Engine Coolant Temperature (ECT) Circuit-High Voltage

Step
Action
Value(s)
Yes
No
1
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check ?
--
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check for 2.4L or Powertrain On Board Diagnostic (OBD) System Checkfor 2.2L
2

1. <LI type=1>Turn ON the ignition switch leaving the engine OFF.
2. Install a scan tool.

Is the ECT sensor value less than the specified value?
-30°C (-22°F)
Go to Step 4
Go to Step 3
3

1. <LI type=1>Review the Freeze Frame data and record the parameters. <LI type=1>Start the engine.
2. Operate the engine within the Freeze frame conditions and Conditions For setting the DTC as specified in the supporting text.

Is the ECT sensor value less than the specified value?
-30°C (-22°F)
Go to Step 4
Go to Diagnostic Aids
4

1. <LI type=1>Turn OFF the ignition switch. <LI type=1>Disconnect the ECT sensor electrical connector. <LI type=1>Connect a fused jumper wire between the following circuit terminals at the ECT electrical connector:
   - ECT sensor signal circuit terminal
   - ECT sensor ground circuit terminal
2. Turn ON the ignition switch leaving the engine OFF.

Is the ECT sensor value greater than the specified value?
130°C (266°F)
Go to Step 6
Go to Step 5
5
Connect a fused jumper wire to the ECT sensor signal circuit terminal at the ECT sensor electrical connector to chassis ground.
Is the ECT sensor value greater than the specified value?
130°C (266°F)
Go to Step 7
Go to Step 8
6

1. <LI type=1>Turn OFF the ignition switch. <LI type=1>Check for poor electrical connections at the ECT sensor electrical connector.
2. Repair the electrical connections as necessary. Refer to Connector Repairs in Wiring Systems.

Was a repair necessary?
--
Go to Step 12
Go to Step 10
7

1. <LI type=1>Turn OFF the ignition switch. <LI type=1>Check for an open in the ECT sensor ground circuit.
2. Repair the ECT ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?
--
Go to Step 12
Go to Step 9
8

1. <LI type=1>Turn OFF the ignition switch. <LI type=1>Check the ECT sensor signal circuit for the following conditions:
   - Open circuit
   - Short to voltage
2. Repair the ECT sensor signal circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?
--
Go to Step 12
Go to Step 9
9

1. <LI type=1>Check for the following conditions at the PCM electrical connector:
   - Poor ECT sensor ground circuit terminal
   - Poor ECT sensor signal circuit terminal
2. Replace the terminals as necessary. Refer to Connector Repairs in Wiring Systems.

Did you need to replace any of the terminal?
--
Go to Step 12
Go to Step 11
10
Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement ..
Is the action complete?
--
Go to Step 12
--
11
Replace the PCM. Refer to PCM Replacement .
Is the action complete?
--
Go to Step 12
--
12

1. <LI type=1>Clear the DTCs with the scan tool. <LI type=1>Start the engine. <LI type=1>Idle the engine at the normal operating temperature.
2. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic has ran and passed?
--
Go to Step 13
Go to Step 2
13
Check to see if any additional DTCs are set.
Does the scan tool display any DTCs that you have not diagnosed?
--
Go to the applicable DTC table
System OK

Document ID# 192535
1998 Chevrolet Cavalier

[FShutz]

Thanks for your quick reply, I appreciate it very much. It sounds like you have done your homework. This condition was not a problem at all until I removed the ECT sensor. The problem was originally a EGR valve stuck open code but I didnt know this because it wouldnt throw a code just yet for the egr. I R&R'd the ECT just as a quick check and then replaced the egr valve (& $150 later) at the same time. My original problem went away (rough idle after NOT, hard start, over heating: typical egr signs) but then the fan & chk eng light (PO118) came on & the temp guage quit working. I figured this had to be related to the ECT becasue I really didnt touch anything else. I really dont think I have a bad PCM or wiring problem. Its too coincidental. Do you think its as simple as bleeding the system ? Thanks again very much for your time. Frank

[sceptre99]

Thanks for your quick reply, I appreciate it very much. It sounds like you have done your homework. This condition was not a problem at all until I removed the ECT sensor. The problem was originally a EGR valve stuck open code but I didnt know this because it wouldnt throw a code just yet for the egr. I R&R'd the ECT just as a quick check and then replaced the egr valve (& $150 later) at the same time. My original problem went away (rough idle after NOT, hard start, over heating: typical egr signs) but then the fan & chk eng light (PO118) came on & the temp guage quit working. I figured this had to be related to the ECT becasue I really didnt touch anything else. I really dont think I have a bad PCM or wiring problem. Its too coincidental. Do you think its as simple as bleeding the system ? Thanks again very much for your time. Frank

Hello.

I have an issue that may be similar. My temp at idle is at what it should be, When I put the car in gear and drive under power the temp spikes down drastically. I replaced the thermo 2 times, replaced the temp sensor, replaced the coolant. I use orange coolant gm approved. I had the car running and played with the temp sensor wires carefully and the fan would kick in and out. I think I have a wiring issue. What do you think?