DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control. Chevrolet PJJ 2000

For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The purpose of the engine cooling system is to maintain an efficient engine coolant temperature level during all engine operating conditions. This is accomplished by using a thermostat to regulate the flow of engine coolant from the engine to the radiator. The thermostat allows the engine coolant to warm up faster by not allowing the engine coolant to flow through the radiator until the engine coolant has reached the thermostat regulating temperature. An Engine Coolant Temperature (ECT) sensor monitors the temperature of the engine coolant. The Powertrain Control Module (PCM) uses the Engine Coolant Temperature (ECT) sensor input for the following conditions:

• | Engine control.

• | Enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and is used to determine if the engine has been driven within the conditions that would allow the engine coolant to heat up to the normal thermostat regulating temperature. The diagnostics that use the engine coolant temperature for enabling criteria may not run when expected if the following conditions exists:

• | Engine coolant temperature does not increase normally.

• | Engine coolant does not reach the thermostat regulating temperature.

### Conditions For Running The DTC

• | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0325, P0336, P0420, P0440, P0442, P0446, P0452, P0453, P0480, P0502, P0503, P0506 or P1441 not set.

• | The engine has been running for more than 30 seconds and less than 1200 seconds (20 minutes)

• | The minimum Intake Air Temperature (IAT) is more than -7°C (27°F)

• | The engine coolant temperature at start up is less than 35°C (95°F)

### Conditions For Setting The DTC

• | The average air flow is more than 10 g/sec.

• | The vehicle has traveled more than 0.5 miles over 25 mph.

• | Enough air flow has entered the engine and the engine coolant temperature has not risen to 40°C (104°F) for 30 seconds.

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present.

• | 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.

### 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.

• | Use a scan tool to clear the DTCs.

### Diagnostic Aids

A skewed ECT sensor will cause this DTC code to set.

An intermittent may be caused by the following conditions:

• | Poor electrical connection

• | Rubbed through wire insulation

• | Wire broken inside the insulation

• | Check for a poor electrical connection or a damaged PCM harness. Inspect the ECT sensor signal circuit and the ground circuit terminals for the following conditions:

- | Improper mating

- | Broken locks

- | Improperly formed connectors

- | Damaged terminals

- | A poor terminal to wire connection

- | Damaged harness

• | Perform an intermittent test. If the electrical connections and the harness check OK, monitor a DMM connected between ECT sensor signal circuit and ground circuit terminals while moving the related electrical connectors and the wiring harness. If a malfunction is induced, the resistance reading will change. This may help in order to isolate the location of the malfunction.

• | Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. Allow the engine to fully cool. The ECT sensor and the IAT sensor will read close to the ambient temperature in order to check for a possible skewed ECT sensor.

2. Measure the engine coolant temperature with a thermometer in order to determine what the actual value the ECT sensor should be. Take into consideration if the engine has been operating and if the engine coolant has been warmed without opening the thermostat.

3. This step simulates a DTC P0118. The PCM and wiring are OK if the PCM senses a change.

4. The ECT sensor, the PCM and the wiring have checked OK at this point. Check for a proper thermostat and a proper cooling fan operation.

5. Reprogram the replacement PCM and perform the Crankshaft Position System Variation Learn procedure.

#### DTC P0125-Engine Coolant Temperature (ECT) Excessive Time to Closed Loop Fuel Control

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
2 | Are any other DTCs set? | -- | Go to Diagnostic Trouble Code (DTC) List/Type | Go to Step 3

3

1. Start and idle the engine for 9 minutes.
2. View the Engine Coolant Temperature (ECT) with a scan tool.

Does the engine coolant temperature read at the specified value or higher?

73°C (165°F)

Go to Step 4

Go to Step 5

4

1. Test the thermostat for proper operation. Refer to Thermostat Diagnosis in Engine Cooling.
2. If a problem is found, repair as necessary before going ahead with this diagnostic table.

Did you complete the repair?

--

Go to Step 5

--

5

1. Allow the engine to fully cool to ambient temperature.
2. Turn ON the ignition, with the engine OFF.
3. Install a scan tool.
4. Compare the ECT sensor reading to the IAT sensor reading.

Are the readings within the specified value of each other?

3°

Go to Step 7

Go to Step 6

6

1. Turn OFF the ignition.
2. Disconnect the ECT sensor connector.
3. Measure the resistance across the ECT sensor terminals with a DMM.
4. Compare the ECT sensor value to the actual coolant temperature with the Temperature vs. Resistance table, refer to Temperature Versus Resistance

Does the ECT sensor accurately reflect the actual engine coolant temperature?

--

Go to Step 7

Go to Step 12

7

1. Disconnect the ECT sensor connector.
2. Turn ON the ignition, with the engine OFF.

Does the ECT sensor value measure less than the specified value?

-30°C (-22°F)

Go to Step 8

Go to Diagnostic Aids

8 | Connect a jumper wire between the ECT sensor signal circuit and the ECT sensor ground circuit. Does the ECT sensor value measure greater than the specified value? | 130°C (266°F) | Go to Step 9 | Go to Step 10

9

1. Inspect the following conditions:

• | Low coolant level

• | Proper thermostat operation. Refer to Thermostat Diagnosis in Engine Cooling.

2. If a problem is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Diagnostic Aids

10

1. Turn OFF the ignition.
2. Inspect the following components for poor connections:

• | ECT sensor

• | PCM

3. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

11 | Important:: The replacement PCM must be programmed and the Crankshaft Position Variation procedure must be performed. Refer to Powertrain Control Module Replacement/Programming and Crankshaft Position System Variation Learn . Replace the PCM. Did you complete the replacement? | -- | Go to Step 13 | --
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement Did you complete the replacement? | -- | Go to Step 13 | --

13

1. Use a scan tool to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK