TJT

To all-
I'm getting the P1291 Code. "No temp increase change in heater" Something like that. Anyway, I believe the relay is working & I believe the grid heater is working because the lights dim & the needle in my alternator gauge deflects with each cycle. What do you all think is the cause of this engine light/code being displayed? A bad sensor?
TJT

bent valves

TJT, the P1291 code will show up if the IAT sensor does not detect a rise in temperature with the grid heaters operating. The computer uses the IAT to determine how much the post start cycling of the grid heaters is needed. With your headlights dimming and voltmeter changing, the grids must be working. My guess is the IAT sensor is bad. A bad sensor will also ruin your fuel mileage. How is yours?

TJT

Haven't put on enough miles since the code first appeared 4 days ago. Cleared the code @ that time. Today I started the engine earlier in the morning while it was a bit cooler & the code was back I certainly will check the mileage. I normally get 17-18 in town & 20-22 on the hwy! How much of a drop might I expect? Is the IAT sensor a dealer item only or will just about any parts house have that item? Thanks for your response.
TJT

bent valves

Your mileage seems about normal. I would expect a couple of MPG lower with a bad air temp sensor since the ECM will keep the timing retarded. Before buying a new IAT try unplugging the sensor and removing it. I found a 13/16” or 21mm deep socket is needed to get it out. Then check for carbon build up on the small two-leaded bead inside the sensor. Use brake cleaner for clearing the carbon. If the sensor is coated with carbon fluff it will thermally insulate it from the intake air. And finally, look closely at the two electrical connections on the sensor and wiring harness for oxidation or dirt. A poor connection will confuse the computer.

If after all that the code still comes back, the part number for early 24 valve engines is: Cummins 3408345. A good parts house should be able to get one. The dealer will be more expensive than buying directly from Cummins.

TJT

Dave,
Thanks for the great advice & clear step by step proceedure. I will carefully check the items referenced.
TJT

TJT

Well Dave et. all,
Cleaned the sensor last week. Waited for a cool morning to start the truck & the light came on! Same code. No sensor in any parts house here. Called the Dodge dealer just to get an idea of $ & the parts person told me that part is no longer availabe. Typical for where I live. Called a truck shop & gave them the Cummins # & the part was here the next day. Installed & again waited till today for a cool morning. Again, I appears that all is working. However, after starting & the voltage needle rises, the engine light is back! The grids seem to continue to cycle as the engine loads & the needle deflects but only for 2 - 3 seconds. Maybe only 59-61* out. Any suggestions? Relays? The grids? Part # for the relays? Source??
Thanks again for the help.
TJT

TJT

My thought here was that the relays are burnt or defective & don't stay connected long enough to get the grids heated & therefore air temp up for the sensor to read. Any thoughts?
TJT

patdaly

Could it also be only 1 of the 2 are firing?

I don't know the 24V setup, but perhaps it expects X rise when 1 fires, and Y rise when both fire. On my truck at least, the voltmeter doesn't change a bunch between 1 grid heater on or both on.

TJT

I suppose that could be true. Another question: After starting & running for 1/2 hr or so. Then park for 3 hrs in 59* weather. When starting again, should those grids come on? Seems to me they should. That is enough time for intake manifold temps to lower, the ambient air temp is below the 66* threshold. I notice today that they do not seem to. No signs of current draw. Maybe the realy has finally given up the ghost! Tonight it is supposed to get down to the high 30s low 40s. I'll check again in the morning. What thinks you all?
TJT

bent valves

I’m sorry to hear the new IAT sensor did not help. Looking at my Powertrain Diagnostics Manual, The P1291 code (No temperature rise from intake air heaters) is set when monitoring the IAT during the first 15 seconds of engine operation.

The code is set with the following condition:
-Initial intake air temperature between 0* and 66*
-Battery temperature and intake temperature within 10* of each other
-Time between end of preheat and engine running state is less than 30 seconds
-Engine cranked less than 5 seconds before starting
-Preheat was completed before starting
-Post heat is active

Possible causes:
- IAT sensor (Must be OK now)
- Intake air heater relay
- Intake air heater element
- High resistance cables

The voltage drop between the battery + and intake air heater relay is more than 0.1 volt, repair high resistance cable. (This test may be hard to perform without 2 people.)

When measuring the grid heaters in operation, there must be above 12 volts on the grid with respect to ground. If not replace the relay. (This assumes the batteries are fully charged.)

TJT

Dave,
Thanks for your input. Based on what I saw happening today, I would say there is no post heat active condition. Not even sure with the initial start up. Alternator needle drops to midway between 8 & 14. Engine starts immediately & the needle rises to the 14v level. Just seems to hang there. This is a bit different from what it was showing last week. Anyway, I'll get an extra set of hands & see what v I have @ the grids. Can the relay go bad in increments or do they simply fail? Called Dodge dealer here. No relays in stock. Back ordered since Jan 23. Common failure? Is the relay available from Cummins or dealer only?
TJT

Boilermaker08

I had similar problems with my truck...I still haven't figured it out yet.

I called cummins to order a relay but they told me that it was a dealer only item. I ended up paying $70 at the dealer. Relay did not fix problem for me though

TJT

Boilermaker,
This isn't too incouraging! I'll check the v @ the grids tomorrow. If there is 12+ v there, I guess I'll look @ the the elements. The cables are in very good condition... I think! I'll probably find a cucuracha has invaded my computer & has shorted something out. Thanks for the input. I'm still on the hunt. How long has yours been acting this way? Has it affected anything or caused a problem other than the engine light coming on?
TJT

patdaly

Dude, save your coin, got it from Rock Auto, http:www.rockauto.com

1999 DODGE RAM 2500 PICKUP 5.9L 359cid L6 DIESEL FI Turbo (6) : Electrical-Switch & Relay : Multi Purpose Relay

STANDARD MOTOR PRODUCTS Part # RY441
Heater Air Intake ;OE: 56026842

$51.79

Just bought one last week, even has the Mopar part number stamped on it!

TJT

Ha! Now that is some good info pat! If I can get another set of hands, I'll be checking v & wires tomorrow.
TJT