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^^^ This
Replace the ECT sensor first and see what happens. |
Originally Posted by YelloEye
(Post 7615127)
Have you tried the steps in post 7?
https://www.cobaltss.net/forums/prob...2/#post4283581 It's usually either a coolant temperature sensor or wiring. No, I'm kind of limited in my troubleshooting capability. I couldn't get the link to work either. I will try checking the wiring and maybe go ahead and replace the coolant sensor. The new thermostat seemed to help, just not a complete fix. It seems really odd the way this is engineered. But what do I know! |
All temp readings come from the same sensor, it's a common failure item as the cars get older.
My original LSJ actually had the harness rub through under the manifold when it was still under warranty. I got random spikes/overheating on the gauge, worse when it had been raining. But in general if it's dashed out the sensor is dead/dying. Check the pins in the connector for corrosion and if you're still having problems trace the harness back to the PCM and make sure there's no spots where it rubbed through the sheathing. |
Originally Posted by Bob_LT
(Post 7615133)
Thanks YelloEye.
No, I'm kind of limited in my troubleshooting capability. I couldn't get the link to work either. I will try checking the wiring and maybe go ahead and replace the coolant sensor. The new thermostat seemed to help, just not a complete fix. It seems really odd the way this is engineered. But what do I know!
Originally Posted by rukkee
(Post 4283581)
This might not help but this is GM's diagnostic instructions for that code. I am NOT a TECH
DTC P0128 Diagnostic Instructions • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. • Review Strategy Based Diagnosis for an overview of the diagnostic approach. • Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptors DTC P0128: Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature Diagnostic Fault Information Circuit Short to Ground High Resistance Open Short to Voltage Signal Performance ECT Sensor Signal P0117 P0118 P0118 P0118 P0116, P0128 Low Reference -- P0118 P0118 P0118 P0128 Typical Scan Tool Data ECT Sensor Temperature Circuit Normal Range Short to Ground Open Short to Voltage ECT Sensor Signal -39 to +120°C (-38 to +248°F) 150°C (302°F) -40°C (-40°F) -40°C (-40°F) Low Reference -- -- -40°C (-40°F) -40°C (-40°F) Circuit/System Description The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT sensor signal circuit and supplies a ground to the low reference circuit. The purpose of this diagnostic is to analyze the performance of the thermostat, by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also meet the calibrated target temperatures under various operating conditions. The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated , and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures. Conditions for Running the DTC • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0502, P0503 are not set. • The start-up IAT is between -7 to +55°C (+19 to +131°F). • The start-up ECT is less than 50°C (122°F) when the start-up IAT is less than 10°C (50°F). OR • The start-up ECT is less than 75°C (167°F) when the start-up IAT is greater than 10°C (50°F). • The engine run time is between 30 seconds and 30 minutes. • The vehicle has traveled greater than 0.8 kilometers (0.5 miles) at greater than 8 km/h (5 mph). • The mass air flow (MAF) average is greater than 1 g/s. • This DTC runs once per ignition cycle within the enabling conditions. Conditions for Setting the DTC • The ECM detects that the minimum ECT of 55°C (131°F) has not been met with a start-up IAT of less than 10°C (50°F). • The ECM detects that the minimum ECT of 80°C (176°F) has not been met with a start-up IAT of greater than 10°C (50°F). Action Taken When the DTC Sets DTC P0128 is a Type B DTC. Conditions for Clearing the MIL/DTC DTC P0128 is a Type B DTC. Diagnostic Aids • DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation. • Inspect the ECT sensor terminals and the ECT harness connector for corrosion. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. • This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures between -7 to +80°C (+19 to +176°F), then compare those measurements to the Temperature vs Resistance table. Refer to Temperature Versus Resistance . • A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference • Engine Controls Connector End Views • Engine Control Module Connector End Views Electrical Information Reference • Circuit Testing • Connector Repairs • Testing for Intermittent Conditions and Poor Connections • Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference • Scan Tool Data List • Scan Tool Output Controls • Scan Tool Snapshot Procedure Circuit/System Verification Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire. •Turn OFF the ignition. •Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling . •If the ignition has been OFF for 8 hours or greater , the ECT and the IAT should be within 15°C (27°F) of each other and also the ambient temperature. Turn ON the ignition, with the engine OFF, and use a scan tool to observe the IAT and the ECT sensor parameters. •Use the scan tool to verify the proper operation of the engine cooling system fans. Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC. •Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis . Circuit/System Testing Important: All electrical components and accessories must be turned OFF and allowed to power down. •Ignition OFF, disconnect the ECT harness connector at the ECT sensor. •Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal A and ground. ⇒ If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. •Ignition ON, verify the scan tool ECT Sensor parameter is less than -39°C (-38°F). ⇒ If greater than the specified range, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the ECM. •Install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool ECT Sensor parameter is greater than 149°C (300°F). ⇒ If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. •If the circuits test normal, test the ECT sensor. Component Testing Measure and record the resistance of the ECT sensor at various ambient temperatures, then compare those measurements to the Temperature vs Resistance table. Refer to Temperature Versus Resistance . Repair Instructions Perform the Diagnostic Repair Verification after completing the diagnostic procedure. • Engine Coolant Temperature Sensor Replacement • Engine Coolant Thermostat Replacement • Control Module References for ECM replacement, setup, and programming © 2009 General Motors Corporation. All rights reserved. |
Seems, like there is something wrong, with the electricity.
Originally Posted by rukkee
(Post 4283581)
This might not help but this is GM's diagnostic instructions for that code. I am NOT a TECH
DTC P0128 Diagnostic Instructions • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. • Review Strategy Based Diagnosis for an overview of the diagnostic approach. • Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptors DTC P0128: Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature Diagnostic Fault Information Circuit Short to Ground High Resistance Open Short to Voltage Signal Performance ECT Sensor Signal P0117 P0118 P0118 P0118 P0116, P0128 Low Reference -- P0118 P0118 P0118 P0128 Typical Scan Tool Data ECT Sensor Temperature Circuit Normal Range Short to Ground Open Short to Voltage ECT Sensor Signal -39 to +120°C (-38 to +248°F) 150°C (302°F) -40°C (-40°F) -40°C (-40°F) Low Reference -- -- -40°C (-40°F) -40°C (-40°F) Circuit/System Description The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT sensor signal circuit and supplies a ground to the low reference circuit. The purpose of this diagnostic is to analyze the performance of the thermostat, by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also meet the calibrated target temperatures under various operating conditions. The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated , and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures. Conditions for Running the DTC • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0502, P0503 are not set. • The start-up IAT is between -7 to +55°C (+19 to +131°F). • The start-up ECT is less than 50°C (122°F) when the start-up IAT is less than 10°C (50°F). OR • The start-up ECT is less than 75°C (167°F) when the start-up IAT is greater than 10°C (50°F). • The engine run time is between 30 seconds and 30 minutes. • The vehicle has traveled greater than 0.8 kilometers (0.5 miles) at greater than 8 km/h (5 mph). • The mass air flow (MAF) average is greater than 1 g/s. • This DTC runs once per ignition cycle within the enabling conditions. Conditions for Setting the DTC • The ECM detects that the minimum ECT of 55°C (131°F) has not been met with a start-up IAT of less than 10°C (50°F). • The ECM detects that the minimum ECT of 80°C (176°F) has not been met with a start-up IAT of greater than 10°C (50°F). Action Taken When the DTC Sets DTC P0128 is a Type B DTC. Conditions for Clearing the MIL/DTC DTC P0128 is a Type B DTC. Diagnostic Aids • DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation. • Inspect the ECT sensor terminals and the ECT harness connector for corrosion. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. • This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures between -7 to +80°C (+19 to +176°F), then compare those measurements to the Temperature vs Resistance table. Refer to Temperature Versus Resistance . • A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference • Engine Controls Connector End Views • Engine Control Module Connector End Views Electrical Information Reference • Circuit Testing • Connector Repairs • Testing for Intermittent Conditions and Poor Connections • Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference • Scan Tool Data List • Scan Tool Output Controls • Scan Tool Snapshot Procedure Circuit/System Verification Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire. •Turn OFF the ignition. •Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling . •If the ignition has been OFF for 8 hours or greater , the ECT and the IAT should be within 15°C (27°F) of each other and also the ambient temperature. Turn ON the ignition, with the engine OFF, and use a scan tool to observe the IAT and the ECT sensor parameters. •Use the scan tool to verify the proper operation of the engine cooling system fans. Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC. •Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis . Circuit/System Testing Important: All electrical components and accessories must be turned OFF and allowed to power down. •Ignition OFF, disconnect the ECT harness connector at the ECT sensor. •Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal A and ground. ⇒ If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. •Ignition ON, verify the scan tool ECT Sensor parameter is less than -39°C (-38°F). ⇒ If greater than the specified range, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the ECM. •Install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool ECT Sensor parameter is greater than 149°C (300°F). ⇒ If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. •If the circuits test normal, test the ECT sensor. Component Testing Measure and record the resistance of the ECT sensor at various ambient temperatures, then compare those measurements to the Temperature vs Resistance table. Refer to Temperature Versus Resistance . Repair Instructions Perform the Diagnostic Repair Verification after completing the diagnostic procedure. • Engine Coolant Temperature Sensor Replacement • Engine Coolant Thermostat Replacement • Control Module References for ECM replacement, setup, and programming © 2009 General Motors Corporation. All rights reserved. |
Originally Posted by Randall Flagg
(Post 7714521)
Wiring. Check it.
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