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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1136 (Engine Cooling System) >> Diagnostic Information and Procedures >> DTC P1258 >> Circuit/System Verification

Circuit/System Verification

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: If DTCs P0480, P0481, P0691, P0692, P0693, or P0694 are set, diagnose those DTCs first.
  1. Observe the engine coolant level. The engine coolant level should be within operating range. Refer to Capacities - Approximate Fluid, and Engine Coolant in the Owner's Manual.
  2. Ensure that the vehicle has the correct engine coolant, with correct concentration, and is not old, contaminated or contains additives. Refer to Recommended Fluids and Lubricants in the Owner's Manual.
  3. Inspect the cooling system for the following:
    • Cooling system leaks
    • Kinked or pinched hoses, especially at the radiator
    • Loose, missing, or damaged radiator air seals or deflectors
    • The radiator and A/C condenser for any air flow obstructions or bent fins. Refer to Symptoms - Engine Cooling .
    4. IMPORTANT: A small delay occurs before the ECM changes the cooling fan speed.
  4. Command the cooling fans in both low and high speed.
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