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IBMobile

P1291 With grid heats disconnected

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I've been starting the engine with the grid heaters disconnected for 6 weeks with morning temps ranging from 28°-55°F with just a little white smoke and a loping idle for about 30 seconds.   This afternoon, after my wife drove it this morning, the check engine light was on.  I scanned the system with an OBD code reader and fond this, P1291 No temp rise from intake heaters. 

Monitor & Set Conditions

Temperature rise from intake air heaters is monitored for first 15 seconds of engine operation. DTC may be stored if initial Intake Air Temperature (IAT) sensor reading is 0-66°F (-17.8 to 18.8°C), Battery Temperature Sensor (BTS) and IAT sensor are within 10°F of each other, time between end of preheat and engine run state is less than 30 seconds, engine is cranked for less than 5 seconds before engine starts, preheat is completed before engine starts, post-heat is active and no IAT sensor or intake air heater relay DTCs exist.

 

This shows that a code, under the right temp conditions, can still be set with the ECM still closing the rely but the main power to the grids disconnected from the battery.  

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15 hours ago, IBMobile said:

I've been starting the engine with the grid heaters disconnected for 6 weeks with morning temps ranging from 28°-55°F with just a little white smoke and a loping idle for about 30 seconds.   This afternoon, after my wife drove it this morning, the check engine light was on.  I scanned the system with an OBD code reader and fond this, P1291 No temp rise from intake heaters. 

Monitor & Set Conditions

Temperature rise from intake air heaters is monitored for first 15 seconds of engine operation. DTC may be stored if initial Intake Air Temperature (IAT) sensor reading is 0-66°F (-17.8 to 18.8°C), Battery Temperature Sensor (BTS) and IAT sensor are within 10°F of each other, time between end of preheat and engine run state is less than 30 seconds, engine is cranked for less than 5 seconds before engine starts, preheat is completed before engine starts, post-heat is active and no IAT sensor or intake air heater relay DTCs exist.

 

This shows that a code, under the right temp conditions, can still be set with the ECM still closing the rely but the main power to the grids disconnected from the battery.  

Very interesting. Mine are disconnected and we don't get much cold weather down. I have started with temps in the 30's with no code. Probably like @Mopar1973Man suggested. Non CA truck & newer.

 

L8tr

D

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I have had my grid heaters disconnected since December 2017. If the temperatures were lower than 32*F I would plug in the block heater hour before leaving. Then all day long with the temperature between ZERO and +20*F I would just start and go. The block still would have residual warm and start easy but never thrown a code or had a starting issue. 

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