Acadia DTC P0128 User Manual

DTC P0128

2017 GMC Truck Acadia (VIN N) | Acadia VIN N Service Manual 9371116 | Document ID: 4734943

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 Descriptor

Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature

Diagnostic Fault Information

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Signal

P0117,

P0119

P0118,

P0119

P0118*,

P0119

P0119,

P0128

Low Reference —

P0118,

P0119**

*

P0119,

P0128

* Internal control module or component damage may occur if the circuit shorts to B+.
** Additional DTCs may set.

Typical Scan Tool Data

ECT Sensor

Circuit

Short to

Ground Open

Short to

Voltage

Operating Conditions: Engine Running at various operating conditions
Parameter Normal Range: Varies with coolant temperature within a range of −39 to 149°C

(−38 to 300°F)

Signal 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 control module (ECM) monitors the temperature of the engine coolant for engine control
and enabling criteria for some diagnostics. The ECM estimates the amount of energy generated to
calculate a target engine coolant temperature (ECT). If the ECT fails to reach the thermostat
regulating temperature, before a predetermined amount of energy is generated engine, the DTC
sets.

Conditions for Running the DTC

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DTC P0068, P0071, P0072, P0073, P0074, P0101, P0102, P0103, P0111, P0112, P0113,
P0114, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0222, P0223, P0502, P0503,
P1101, P1516, P2101, or P2135 is not set.

The start-up ECT is between −40° and 66°C (–40° and 151°F).

The engine OFF time is greater than 30 min.

The engine run time is between 2 and 24 min.

The vehicle has traveled greater than 2.4 km (1.5 mi).

The ethanol in the fuel is less than 87%.

This DTC runs once per ignition cycle when the above conditions are met.

Conditions for Setting the DTC

The ECM determines that the ECT has not met its calibrated target of 71°C (160°F) when the
start-up ambient temperature was between 10 and 52°C (50 and 126°F), for greater than 1 s.

OR

The ECM determines that the ECT has not met its calibrated target of 55°C (131°F) when the
start-up ambient temperature was between –7 and 10°C (19 and 50°F), for greater than 1 s.

Action Taken When the DTC Sets

DTC P0128 is a Type B DTC.

The engine coolant temperature gauge defaults to cold.

The A/C is commanded OFF and inoperative.

The cooling fans are commanded ON.

The Driver Information Center (DIC) may indicate a steering assist reduced message.

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.

Corrosion in the ECT sensor terminals or the ECT harness connector results in a greater
voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.

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

Component Connector End Views

Component View Reference

Powertrain Component Views