Buick Regal: DTC P1258
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 P1258
Engine Coolant Overtemperature - Protection Mode Active
Circuit/System Description
The engine control module (ECM) uses the engine coolant temperature sensor to
monitor the engine for an
over-temperature condition. This condition occurs when the coolant temperature
is above a calibrated
value. The ECM will alternately disable 2 groups of cylinders by turning OFF the
fuel injectors. By
switching between the 2 groups of cylinders, the ECM is able to reduce the
temperature of the coolant.
Conditions for Running the DTC
- The engine is operating for greater than 30 seconds.
- DTC P1258 runs continuously once the conditions above have been met.
Conditions for Setting the DTC
The ECM detects that engine coolant temperature is warmer than 131ºC
(268ºF) for greater than 2
seconds.
Action Taken When the DTC Sets
- DTC P1258 is a Type A DTC.
- The engine will operate in the Overheated Engine Protection Operating
Mode.
- The IP will illuminate the coolant temperature indicator lamp and the
driver information center
(DIC), if equipped, may display a message.
- If the protection mode is active and an ECT sensor DTC sets, the
protection mode will remain active
at the start of the next drive cycle until the ECT sensor DTC runs and
passes.
Conditions for Clearing the MIL/DTC
DTC P1258 is a Type A DTC.
Reference Information
Schematic Reference
Engine Controls Schematics (LGX)
Connector End View Reference
Component Connector End View Index
Description and Operation
- Cooling Fan Description and Operation
- Instrument Cluster Description and Operation
- Indicator/Warning Message Description and Operation
Electrical Information Reference
- Circuit Testing
- Connector Repairs
- Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
K20 Engine Control Module: Scan Tool Information for scan tool
information
Circuit/System Verification
1. Ignition ON.
2. Verify DTC P0480, P0481, P0691, P0692, P0693, or P0694 is not set.
Refer to DTC P0480, P0481, P0691, P0692, P0693, or P0694 (LTG) or DTC
P0480, P0481,
P0691, P0692, P0693, or P0694 (LGX).
- Go to next step: If no DTCs is set
NOTE: A short delay occurs before the ECM changes the cooling fan
speed.
3. Verify the cooling fan operates at each available speed as commanded with
a scan tool.
- Cooling fan does not operate
Refer to Cooling Fan Inoperative (LGX) or Cooling Fan Inoperative (LTG).
- Go to next step: Cooling fan operates
4. Verify that the engine does not overheat.
Refer to Engine Overheating.
- Go to next step: Engine does not overheat
5. Operate the vehicle within the Conditions for Running the DTC.
Refer to Symptoms - Engine Cooling.
- Go to next step: If the DTC does not set
6. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic
procedure.
READ NEXT:
Important Preliminary Inspections Before Starting
Before using the Symptom diagnosis, perform the following:
Perform Diagnostic System Check - Vehicle and verify all of the
following items:
Engi
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.
Diag
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.
Diag
SEE MORE:
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service. For additional
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Warning:
Poorly maintained and
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FRONT SUSPENSION DESCRIPTION AND OPERATION
The front suspension has 2 primary purposes:
Isolate the driver from irregularities in the road surface.
Define the ride and handling characteristics of the vehicle.
The front suspension absorbs the impact of the tires travelling over
irregular road su