P1258

Code

GM P — Powertrain

Engine Coolant Overtemperature Protection Mode Active

Brand: GM

Type: P — Powertrain

Views: UK: 30 EN: 76 RU: 33

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Low coolant level or air trapped in cooling system
Faulty coolant temperature sensor (CTS) or wiring/connector issues
Stuck-closed thermostat or failed thermostat that does not open
Cooling fan(s) not operating (fan motor, relay, fuse, wiring, fan control)
Radiator blockage, collapsed hose, or restricted coolant flow
Failed water pump or broken drive belt

Symptoms

Cooling system warning lamp or temperature gauge in the red/high zone
Reduced engine power / limp-home mode activated
Cooling fans running continuously or not running when commanded
Possible engine misfire, poor performance, or battery/charging system reduced output if ECM limits alternator
Visible coolant leaks, steam, or unusual smell from engine bay

What to check

Connect a scan tool and read freeze frame and live data for coolant temperature and fan commands
Verify and record stored codes and pending codes in PCM/BCM
Visually inspect coolant level and reservoir condition (only when cold)
Check for obvious coolant leaks, collapsed hoses, or damaged radiator
Observe fan operation with engine cold start and during warmup; command fans ON via scan tool if available
Inspect fan fuses and relays and test fan motors directly if needed

Signal parameters

Coolant temperature (ECT) — overtemperature usually > ~120°C (248°F) when the code triggers (vehicle-specific)
CTS voltage range: ~0.1–5.0 V typical (varies with temp); compare live voltage to expected at ambient temp
Fan control duty or commanded ON status from PCM (ON/OFF or PWM duty % when commanded)
Thermostat open temperature specification (vehicle-specific, commonly 82–105°C)
Radiator pressure cap retention and system pressure during pressure test (compare to cap rating)

Diagnostic algorithm

Step 1 — Retrieve codes and freeze frame data: use a capable scan tool to capture ECT at time of fault, fan command status, and related codes (P0117/P0118/P0217/P0128).
Step 2 — Visual/basic checks: with engine cold check coolant level, hoses, radiator fins, belts, and signs of leaks or steam. Top up if low and burp air from the system per service procedure.
Step 3 — Verify fan operation: run engine to warm up under safe conditions and command fans ON via scan tool. If fans do not run, check fuses/relays, fan motor power/ground, and PWM outputs from controller. Repair wiring or replace faulty components.
Step 4 — Check thermostat and coolant flow: measure temperature at thermostat housing and radiator inlet/outlet during warm-up. If thermostat stays closed above specified temperature, replace thermostat.
Step 5 — Test the coolant temperature sensor/circuit: compare CTS resistance or voltage to specification at known temperatures. Wiggle test connector and inspect for corrosion; repair wiring or replace sensor as needed.
Step 6 — Pressure test cooling system: use a hand pump to pressurize system to cap rating and inspect for leaks, collapsed hoses, or radiator blockage. Verify radiator cap function.
Step 7 — Check for combustion leakage: if overheating occurs with coolant loss or unexplained pressure, perform a block test (combustion gas test) to rule out head gasket or cracked head/block.
Step 8 — Inspect water pump and drive: check for bearing noise, coolant leakage at pump seal, and correct coolant circulation. Replace pump if failed.
Step 9 — Repair/replace the faulty component(s), clear codes, and perform a controlled road test to verify temperature remains in normal range and no reoccurrence of P1258.
Step 10 — If intermittent and no mechanical cause found, inspect PCM/BCM grounds and power feeds and review technical service bulletins for application-specific issues.

Likely causes

Low coolant level or air in the system
Cooling fan(s) inoperative or fan control failure
Stuck or failed thermostat
Faulty coolant temperature sensor or poor electrical connection

Fault status

⚠️ Status

ECM detected coolant overtemperature condition and activated engine protection mode.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

Similar codes

Your experience will help others

+100 karma for a short comment :)

Was this AI description helpful?

Your feedback helps improve AI descriptions.

👍 Like 0 👎 Dislike 0

Send to email