Throwing all kinds of codes after passenger airbag replaced on recall

[gerry]

Immediately after the passenger airbag was replaced on my 2004 3500 dually, within two miles the brake/abs light flashed on and off, service 4 wheel drive sign came on then off, airbag flashed on. low fuel warning flashed on and off, in short just about all the warning lights came on then off and have continued to do so. I turned around and took it back to the dealer who said it was nothing they did even though it was fine before they replaced the airbag, and they say it was coincidental and almost certainly caused by my Smarty Jr. This sounds like crap to me but has anybody else had this issue with or without the airbag recall? Any thoughts? I think the dealer hasn't got a clue but where else is there anyone that knows these ''modern'' electronics?

 

[6speed]

I had my air bags replaced. I have the Smarty S06, No CEL's here. I have not been into the ECM since they did it. Take the Smarty off and see what happens, Only guessing, but maybe they tried to update the ECM with the airbag info and the Smarty "may" been a block of some sort. But mine was done and I have nothing lighting up.

 

[Bob4x4]

Check the connector at the module on the floor(hump)

 

[gerry]

Bob4x4
Can you give me a better idea where on the hump to look, and thanks for the help. All the dealer could say was their experience shows that chips and programmers tend to lead to electrical problems which I think is their way of saying they don't have a clue.

 

[Bob4x4]

It sits on top of the hump,under the lower dash.acess depends on stick/auto center console

 

[Prairie Dog]

I wonder if there's a defect in the new AB's electronics and it's pulling a buss down.
If you were to unplug the bag and everything starts working, you have your fault.

 

[Bob4x4]

I wonder if there's a defect in the new AB's electronics and it's pulling a buss down.
If you were to unplug the bag and everything starts working, you have your fault.

Never seen that happen...

 

[gerry]

Thank you all for your help. The dealer after telling me that in their 20+ years of experience have found that chips/programmers cause most of the electrical glitches and keeping the truck two weeks figured out that unplugging the fan clutch caused it to stopped throwing codes! And when I asked how much to fix that they said $890! I said I would pick the truck up and take care of it. My usual mechanic quoted me $430. When I picked up the truck and drove it 15 miles home with the fan clutch disconnected no codes. It only took them two weeks to diagnose so I don't think I will be returning to them for anything.

 

[TConver]

Use a mopar fan clutch, the aftermarket ones tend to be junk.

 

[Prairie Dog]

Never seen that happen...

Same thing that happens when the fan clutch malfunctions or is damaged and causes all kinds of odd faults and codes - a scenario that is well known to those who have been here a long time.
It turns out I was close. The fan clutch was causing an issue on the bus.

 

[sag2]

Same thing that happens when the fan clutch malfunctions or is damaged and causes all kinds of odd faults and codes - a scenario that is well known to those who have been here a long time.
It turns out I was close. The fan clutch was causing an issue on the bus.

I'm pretty sure he was speaking to your air bag controller comment. He knows all about what happens when the fan clutch wiring is damaged. He has probably replaced more fan clutches than all of us combined on TDR.

And FYI, there are no BUS wires going to the fan clutch. It's the 5v circuit that gets shorted and causes all the problems.

 

[Prairie Dog]

I'm pretty sure he was speaking to your air bag controller comment. He knows all about what happens when the fan clutch wiring is damaged. He has probably replaced more fan clutches than all of us combined on TDR.

And FYI, there are no BUS wires going to the fan clutch. It's the 5v circuit that gets shorted and causes all the problems.

What is that 5v doing (it goes to the clutch fan right?) and how does the computer know when the clutch fan is bad?

BTW, I've been around a while too.

 

[verk]

What is that 5v doing (it goes to the clutch fan right?) and how does the computer know when the clutch fan is bad?

BTW, I've been around a while too.

My guess is that there a hall sensor and reluctor ring inside the fan assembly and this is how it monitors speed ensuring that what the ECM outputs (i.e. PWM ) matches actual fan speed. If they don't a DTC is set. Be nice to know from somebody that actually knows.

 

[sag2]

My guess is that there a hall sensor and reluctor ring inside the fan assembly and this is how it monitors speed ensuring that what the ECM outputs (i.e. PWM ) matches actual fan speed. If they don't a DTC is set. Be nice to know from somebody that actually knows.

You are correct, there is a speed sensor (3 wire, 5v, ground, sensor signal) in the fan that reports actual fan speed back to the engine so it can compare that to desired fan speed. Most 5v circuits on FCA vehicles feed more than one sensor, so when the 5v gets shorted to ground or battery it takes down any other associated sensors.

 

[sag2]

My guess is that there a hall sensor and reluctor ring inside the fan assembly and this is how it monitors speed ensuring that what the ECM outputs (i.e. PWM ) matches actual fan speed. If they don't a DTC is set. Be nice to know from somebody that actually knows.

You are correct, there is a speed sensor (3 wire, 5v, ground, sensor signal) in the fan that reports actual fan speed back to the engine so it can compare that to desired fan speed. Most 5v circuits on FCA vehicles feed more than one sensor, so when the 5v gets shorted to ground or battery it takes down any other associated sensors.

 

[sag2]

What is that 5v doing (it goes to the clutch fan right?) and how does the computer know when the clutch fan is bad?

BTW, I've been around a while too.

I have been around a couple years myself, and I still only know a fraction of what's out there. That's what's nice about a forum with many people, someone has the information, or has experienced the condition before and can share the knowledge with the rest.

 

[sag2]

What is that 5v doing (it goes to the clutch fan right?) and how does the computer know when the clutch fan is bad?

BTW, I've been around a while too.

I have been around a couple years myself, and I still only know a fraction of what's out there. That's what's nice about a forum with many people, someone has the information, or has experienced the condition before and can share the knowledge with the rest.

 

[Prairie Dog]

I'll answer my question.
The clutch fan uses 5V which is Vcc from the computer. (it may even use 12V and knock it down, I don't know) The clutch fan, like all discrete components, uses that 5v to power its electronics and create a simple signal the computer can read as speed. In one of the CF's failure modes, it shorts or more accurately, pulls down that 5V - certainly this is not a failure mode Dodge intended to happen but it happens. Since many other discrete components/sensors are also powered by Vcc, anything powered by that same 5v that the computer derives DATA from are effected.
All the sensors around the truck are simple digital components of a computer circuit (some may be or analog components that convert to digital through D to A converters).
The 5V itself is not a bus but the signals created by items powered by it are effected. The output of these components are on various busses. With digital circuits, a low Vcc means they may go to a hi (least likely), low or tri-state (unstable area between hi and low) output which can wreak havoc on a data bus.
This is why a failed item on the truck effects something else that is seemingly unconnected.

Scott

 

[Prairie Dog]

I'll answer my question.
The clutch fan uses 5V which is Vcc from the computer. (it may even use 12V and knock it down, I don't know) The clutch fan, like all discrete components, uses that 5v to power its electronics and create a simple signal the computer can read as speed. In one of the CF's failure modes, it shorts or more accurately, pulls down that 5V - certainly this is not a failure mode Dodge intended to happen but it happens. Since many other discrete components/sensors are also powered by Vcc, anything on that buss that the computer derives DATA from are effected.
All the sensors around the truck are simple digital components of a computer circuit (some may be or analog components that convert to digital through D to A converters).
The 5V itself is not a bus but the signals created by items powered by it are effected. The output of these components are on various busses. With digital circuits, a low Vcc means they may go to a hi (least likely), low or tri-state (unstable area between hi and low) output which can wreak havoc on a data bus.
This is why a failed item on the truck effects something else that is seemingly unconnected.

Scott

 

[verk]

I agree with general sentiments, I've learned an incredible amount from this forum. This thread was helpful for me to realize why this component failure creates a knock-on effect. Looking further at the service manual, I see a splice ( shares ground with other modules ) on the SENSOR GROUND wire of fan drive speed sensor. Is this the reason this failure mode of fan drive effects other circuits or is it something internal to ECM or something else entirely?

As for understanding the circuit I've looked at the wiring diagram and think I understand the fan drive. The fan drive has two discrete circuits: a 12V low-side driver that utilizes PWM to control speed and a 3 wire 5V speed sensor wire that most likely uses a Hall effect sensor although the manual doesn't say.