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Discussion Starter #1
I put a lsj thermostat in and bout a couple weeks later the code popped up and my temp is blank. Checked the plug it's plugged in. But when the dash temp is blank I Can still get a temp on my phone through the torque app. Any ideas? Could it be running too cold?

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Looks like it's not falling into parameters set by PCM. If a code related to temperature is set your DIC will show ------- How hot does it run on highway?

DTC P0128
Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach the regulating temperature of the thermostat, the diagnostics that use ECT as enabling criteria may not run when expected.

If the PCM detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.

DTC Descriptor
This diagnostic procedure supports the following DTC:

DTC P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature

Conditions for Running the DTC
• DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0502, P0503 are not set.

• The startup ECT is less than 50°C (122°F) when the IAT is greater than 10°C (50°F), or the start-up ECT is less than 65°C (149°F) when the IAT is less than 10°C (50°F).

• The intake air temperature (IAT) is more than -7°C (+19°F).

• The engine run time is between 30 seconds and 30 minutes.

• The vehicle is driven more than 0.8 kilometers (0.5 miles) at more than 8 km/h (5 mph).

• The mass air flow (MAF) is between 2-30 g/s, with the average more than 1 g/s.

• This DTC runs once per ignition cycle within the enabling conditions.

Conditions for Setting the DTC
The PCM detects that:

• The calibrated amount of engine run time has been met

• The calibrated amount of engine air flow has been met

• The calibrated vehicle speed and distance have been met.

• The calibrated ECT of 55°C (131°F) with a start-up IAT greater than 10°C (50°F) has not been met.

OR

• The calibrated ECT of 70°C (158°F) with a start-up IAT less than 10°C (50°F) has not been met.

Action Taken When the DTC Sets
• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.
 
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