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.  

I guess that would make it rare but possible. 

Difference in of ECM software. Like my 2002 does not trip the P1291 code like your truck. It could be difference in California software too. Like my truck is federal software.

Edited May 18, 20186 yr by Mopar1973Man

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

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. 

Mine did it every time.  I hooked it back up.

Seems like the early years have this issue of the P1291 code. 

 Mine has not set a code for this since I disconnected them 2.5 years ago.

I'm having the same issue.  California truck...98.5.  Grids disconnected and throwing the P1291.  

Talk to @IBMobile he got an idea on how to fool the grid heaters without throwing a code.

On 5/18/2018 at 6:09 AM, Mopar1973Man said:

Difference in of ECM software. Like my 2002 does not trip the P1291 code like your truck. It could be difference in California software too. Like my truck is federal software.

 

This is gotta be it right on the money @Mopar1973Man Literally the only "emissions" component on these trucks was the grid heaters so it would make sense for the CA trucks to throw that code where others wont

 

When smogging these in CA they look for evidence of pump tap, intake/exhaust, smoke or snap test, and grid heaters. Thats it.

Edited October 4, 20186 yr by 2000Ram2500
ca smog

Mine just started doing it since the temperature has been dropping.  No issues for the past couple months with the heater disconnected.  

HI All, Mine is a federal and the Grid heaters have been off for a long time.  No Codes.

 

Michael

I've hooked back up the grid heaters on my truck. Now that I've tested my alternator and done the @W-T ground wire mod. I'm going to monitor this winter and see if the alternator holds up better or not.