P1291 No temperature rise seen from intake air heater

[Nomad2015]

Does anyone out there know how to troubleshoot the intake air heater? 

 

 

 

 

 

 

 

 

 

 

 

 

 

[IBMobile]

Check for battery voltage from the driver's side battery to the intake air heater relays. 

If no voltage, check fusible link between the battery and Intake air heater relay.   

If voltage, turn ignition key to the on position and with "wait to start" light illuminated, test for voltage at grid heaters.

If voltage,  check air grid heater grounds at air intake manifold. If good grounds then replace air heater grids.

 

If no voltage at air intake grid heaters remove either the 16-gauge yellow/black or orange/black trigger wire from one of the air heater relays and install voltmeter between the that wire and ground.  Turn ignition key to the on position and with "wait to start" light illuminated, test for voltage.  Test the other air heater relay the same way.   If no voltage, then test for voltage at pins number 29 and 47 at the ECM.  If no voltage, then the ECM is bad and need to be repaired.

 

If there is battery voltage, then place an ohm meter between the black/tan wires at the air heater relays and ground. 

If reading is greater than 0-5 ohms check open circuit or bad grounding.

If reading is 0-5 ohms air heater relay ground is good and air heater relay needs to be replaced   

[Great work!]

Best tool for that is a DC clamp on current meter. Notice DC they cost double what the cheap AC only ones do.

 

The ECU cycles the grid heaters during warm up. It looks the the intake air temperature sensor IAT. When the heater is on and again when the heater is off. It expects to see some temp change differential if not it throws the code.

 

The two heater relays by the battery should click while cycling. They burn up and some times weld in the on state and can burn up the grids, wiring, alternator even burn the truck down.

The relays look like riding lawn mower starter relay but they have a different coil resistance do not use lawn mower parts.

Start with checking the fusible wires on the battery and clean and reconnect the all the heavy wires also check the ground wire on the intake horn. 

If one of the nuts or studs strip or break then you probably found an issue.

[Max Tune]

Tap the dark title. It'd a link to your code...

Edited February 27, 2023 by Max Tune

[jlwelding]

I dont know how much winter you have in Az. but I'll bet you can do away with grid heater completely. I deleted mine and glad of it, battery killing junk is all it is that is if you can get by with it. I live in central Tx and 40 degrees is normal lows. Dont get me wrong we do go through some really bad freezes but 3-4 days later and we're usually back into the 60's. I plug mine in a few times a season and if its that bad Im not taking my diesel anyway. 

[Nomad2015]

Thank you all for your feedback it's been very helpful. I am a full-time Rv'er and I find myself in all kinds of weather. I realize after going throw the info I made some assumptions that led to this problem. About a month ago I noticed my MPG was down about 5 mpg and the truck was very sluggish so I thought injectors the truck has 252k injectors never been replaced. Then a couple of weeks later on a cold morning (38 degrees), I got the P1291 code I had to clear it a couple of times then it warmed up outside ('50s) and the code went away. About a week later I'm a mile or so from home when the check gauges lite came on the only thing I noticed right away was my fuel pressure was 10psi (normal 17-18psi) I got home and noticed the stock volt gauge in the dash was dead no reading so I turned the engine off grabbed my volt tool and plug it in 12v outlet and it came back "battery almost dead" and "alternator overcharging" about this time I look in the engine bay and all I see is yellow smoke pouring out of the alternator I turned the truck off and the smoke was getting worst so I disconnected both the neg. cables off the batteries and the smoke over time started to decrease. 

this is what's been done so far.

Removed the alternator, on inspection notice the pins on the back of the alternator had heavy corrosion and the connector looked cracked on the wire side.

Purchased a new alternator and connector and installed them. have not fired the truck yet.

Purchased 2 new batteries and installed  When I inspected the crossover cable I found a couple of inches of corrosion on each end so I've purchased a new crossover cable and should get it in a couple of days.

What I don't know at this point is whether my PCM is working and I'm tempted to just replace all things intake air heater but if my PCM is dead I might not be able to find a replacement for a while if ever. In which case the truck becomes yard art.

[Great work!]

Pcm controls alternator. ECM on the side of engine controls grid heaters.

Both are difficult to find new used or working properly and programmed to your truck. Eliminate all other possible problems first. One of the relays probably got stuck in the on state and the heavy load of the heater probably overheated the alternator.

[Nomad2015]

1 hour ago, Great work! said:

Pcm controls alternator. ECM on the side of engine controls grid heaters.

Both are difficult to find new used or working properly and programmed to your truck. Eliminate all other possible problems first. One of the relays probably got stuck in the on state and the heavy load of the heater probably overheated the alternator.

Thank you

[Max Tune]

If you find out your pcm is fried, Auto Computer Specialist, they can be found in the vendor section. Tell them you found them on this site.

[Nomad2015]

So I got all the new parts installed and fired the truck up without air intake heaters and alternator output cable connected and I had 60v output at alternator. So it looks like I need to give ACS a call.

[Great work!]

Did you mean alternator disconnected or connected? Unloaded alternators can float pretty high. Make sure the giant fuse is ok and output wire has continuity to battery. Disconnect field wires at back of alternator, output should drop off. Watch battery voltage and momentarily connect field wire if voltage goes over 16 stop. Your PCM could be at fault.

[Nomad2015]

15 hours ago, Great work! said:

Did you mean alternator disconnected or connected? Unloaded alternators can float pretty high. Make sure the giant fuse is ok and output wire has continuity to battery. Disconnect field wires at back of alternator, output should drop off. Watch battery voltage and momentarily connect field wire if voltage goes over 16 stop. Your PCM could be at fault.

With the Truck running the field wires disconnected from the alternator I checked the voltage at the connector and had zero volts. I connected the field wire connector to the alternator and checked the output at the alternator it was 60v. I couldn't find a fuse that referenced the alternator, I did find a 140a fuse and it looked good.

On 2/27/2023 at 2:22 PM, Max Tune said:

If you find out your pcm is fried, Auto Computer Specialist, they can be found in the vendor section. Tell them you found them on this site.

I spoke with ACS this morning and let them know I found them on this website. At this point, I feel like I'm about to gamble with $1k that the PCM will fix the problem. As far as electrical troubleshooting I am pretty much in over my head now. 

[Tractorman]

49 minutes ago, Nomad2015 said:

connected the field wire connector to the alternator and checked the output at the alternator it was 60v.

 

Do not replace any parts yet! 

 

If you are in fact seeing 60 volts DC at the alternator output with everything properly connected, this means that continuity has been lost somewhere between the alternator output and the driver side battery.   The 140 amp fuse is in this path along with the associated wiring. 

 

Use a test light with an incandescent bulb (not a multi-meter) and perform the following test:  With engine switched off, clamp one end of the test light to a battery ground and touch the other end of the test light to the alternator output.  The test light should light up brightly.  If it does not, you now know where to start looking.

 

- John

[Nomad2015]

3 hours ago, Tractorman said:

 

Do not replace any parts yet! 

 

If you are in fact seeing 60 volts DC at the alternator output with everything properly connected, this means that continuity has been lost somewhere between the alternator output and the driver side battery.   The 140 amp fuse is in this path along with the associated wiring. 

 

Use a test light with an incandescent bulb (not a multi-meter) and perform the following test:  With engine switched off, clamp one end of the test light to a battery ground and touch the other end of the test light to the alternator output.  The test light should light up brightly.  If it does not, you now know where to start looking.

 

- John

Thanks, John I had everything properly connected with the exception of the red output cable that was not connected. Is that what's causing the lack of continuity?

[Tractorman]

5 hours ago, Nomad2015 said:

connected with the exception of the red output cable that was not connected

 

Need to be clear here.  There are three connection points on the back of the alternator.  The two small connection points are for the two small field wires.  The large insulated connection point is for the alternator output wire which has an uninterrupted path to the driver side battery.  Is this the wire you left disconnected?  If so, the alternator cannot deliver current to the battery.  In fact, if any of the three wires are left disconnected, the alternator cannot charge the batteries.

 

Also, there may or may not be a ground wire connection on the back of the alternator.

 

- John

[Nomad2015]

11 minutes ago, Tractorman said:

 

Need to be clear here.  There are three connection points on the back of the alternator.  The two small connection points are for the two small field wires.  The large insulated connection point is for the alternator output wire which has an uninterrupted path to the driver side battery.  Is this the wire you left disconnected?  If so, the alternator cannot deliver current to the battery.  In fact, if any of the three wires are left disconnected, the alternator cannot charge the batteries.

 

Also, there may or may not be a ground wire connection on the back of the alternator.

 

- John

So what is the proper way to test alternator output?

 

[Tractorman]

1 minute ago, Nomad2015 said:

So what is the proper way to test alternator output?

 

I was hoping that you were going to answer my question from my previous post.  You also haven't verified that you have battery voltage on the alternator output wire with a test light.   Answering questions and performing tests are very important for moving forward with diagnostics.  At this point, I still don't know which wire you left disconnected and if this wire is still disconnected.

 

Ensure grid heaters are disconnected.  If you have all of the alternator wires connected (the question that is still unanswered) and there is battery voltage at the alternator output terminal (verified with a test light), then start the engine.  If battery voltage rises and steadies at around 14 volts, then the alternator is charging.

 

- John

 

 

[Nomad2015]

18 hours ago, Tractorman said:

 

I was hoping that you were going to answer my question from my previous post.  You also haven't verified that you have battery voltage on the alternator output wire with a test light.   Answering questions and performing tests are very important for moving forward with diagnostics.  At this point, I still don't know which wire you left disconnected and if this wire is still disconnected.

 

Ensure grid heaters are disconnected.  If you have all of the alternator wires connected (the question that is still unanswered) and there is battery voltage at the alternator output terminal (verified with a test light), then start the engine.  If battery voltage rises and steadies at around 14 volts, then the alternator is charging.

 

- John

 

 

Wow harsh, There is no shortage of attitude on this website. Thank you all for your feedback and have a nice day! I'm done with this. 

[Mopar1973Man]

We try to help out where we can. He's right it can be difficult some times to understand what is going on. Suggestion is grab some photos with your phone and post them up then we can see what you talking about.

[Tractorman]

@Nomad2015, I apologize for being "harsh".  That was not my intention.  I will stay out of the discussion and maybe others can help you.

 

- John