So I've been having a reocurring problem with my truck. Everything runs perfectly fine until my car registers it
's check engine code for CODE 24 which is the AFM Temp sensor.

The truck has a new timing chain, NGK spark plugs, Belden wires and new rotor.
Timing is set to to spec
Idle is set to spec and engine hums fine at idle after warmed up
Throttle body is cleaned
TPS is positioned

here is the process of occurence.
- Code cleared, truck drives well other than engine feeling bogged down (I swear it had better pickup a few months ago before the code)
- When taking off or coming to a stop the check engine will light up
- check engine disappears when taking off from a stop or when coming to a full stop
the check engine flashing does NOT happen every single time but like 75% of the time

So I checked the AFM per 4crawlers site and everything checks out perfectly.
-All pins are within range
-opening/closing the door is within range
-no dead spots on the resistive strip

I checked continuity of the harness from the AFM PLUG side to the ECU
ZERO resistance

E2-THA which THA being the temperature pin is within range when HOT or COLD
I have cleaned the temp probe in the chamber and the actual AFM circuit board with Mass Air Flow Cleaner

so what gives? Is there a loose wire somewhere that knocks around? I cannot find a damn thing to fix on this AFM. Any other tests to run?

 

Most likely.

As usual, start with WHAT code 24 tells you: "Open or short in intake air temp. circuit." So it doesn't have anything to do with the plugs, rotor, timing, ....

First you check the temp sensor directly, and you say that THA-E2 is within range. You say you checked the continuity of the harness, so I assume you checked all SIX leads.

While it is possible you have an intermittent open on E1, I would guess it's on THA. I'd put a voltmeter between THA and Ground at the ECM. With Key-On, Engine-Off you should get 0.5-3.4 volts. Then carefully wiggle the harness; tap gently on the VAF. If the voltage swings to 12v you have an open, 0v you have a short.

 

I only checked three of the leads, I cannot find the other three on the ECU pinout chart

what do you mean by ECM ground? Is there a specific pin on my ECM to check?

 

No, it's less likely that E1 VAF-ECM is your problem. But it seems not everyone remembers that voltage is always measured BETWEEN two points, Any convenient ground should work for your "black" voltmeter lead.

That said, you wouldn't be the first person to be bedeviled by an open ground. So measuring from E1 at the ECM is probably a good idea.

 

I tested THA to ground on battery and shook the wire harness

no change

i did THA to E1 on the ECU

no change


the voltage were within the ranges your specified and they were perfectly stable.


Any other ideas?

 

Here is a pic so you know Im not doing it wrong.

 

You did it wrong. You want to test the whole circuit, not just the sensor. The sensor signal to the computer can get lost due do bad wires or loose, dirty connections.

 

I did run it from the E1 on the ECU (backprobing the harness connection)

to THA on the AFM (backprobing the harness connection)

i just didnt snap a picture of that test

same result, steady volts within range



could it be that the temperature probe is simply broken?

could it be a leak in the boot tripping the AFM temp sensor? I see where the boot meets the throttle body there is a split, however there are no cracks in the body itself.

 

That tests the E1 wire from VAF to ECU. Did you also check the THA wire from VAF to ECU? That's the most likely source of your problem.

That's the least likely source of your problem. You have an intermittent open or short. That's what the code tells you. Wires fail that way all the time; solid temperature sensors not so often.

Unfortunately, intermittent anything is always hard to find; it's not broken at the moment you're looking. I suggested wiggling the harness (or tapping on the probe), but you can't wiggle (by hand) every point that might have the problem. You could try driving around with a voltmeter connected (try hot-melt glue) to the THA pin on the ECU. You should see the voltage change (to a point out of range; it SHOULD change with ambient air temp) at the moment something happens.

 

So your saying i should run the voltmeter from the VAFM THA pin going to the THA pin on the ECU?

i have not done that one yet

im still learning the dynamica of sensors, grounds etc

 

So I went E1 on the AFM

to

THA on the ECU

and i finally got my voltage to jump around by hitting the cords just after the AFM plug

it stays at 2.5 and when I hit it I got it to go to 0 a few times

now when I try to recreate the issue it jumps to 5.0 and stays

 

Now make sure the plug is clean bright metal, and tight to the AFM (tighten up the female lug inside there)

 

So I retightened the AFM Lug connections and the problem hasn't came back. I only test drove it around the block. I will write here to let you know if the problem arises again.

Thank You so far