DEF pump circuit
This is my first Ram diesel exhaust fluid pump issue. Code is P208A for Reductant pump A control circuit open. Schematic shows PhaseA, PhaseB, and Phase C. Diagnostic chart recommends unplugging pump and install jumper wire from Phase A to Phase B then as a second test from Phase A to Phase C. Both of these tests should result in P208A going inactive and P208D REDUCTANT PUMP CONTROL CIRCUIT HIGH should become active. I have tried this and am very unsuccessful in manipulating the codes set, always resets after code clear even with jumper wire installed.
I measured the voltage coming out of module, 0V on Phase B and C, 3.5V on phase A. I measured resistance on pump PhaseA-PhaseB = 3500ohms, PhaseA-PhaseC = 350Ohms, PhaseB-PhaseC =0ohms. I have not load tested wiring between module and pump but have measured continuity =0ohms.
Now my question for anyone familiar with this setup, is my pump indeed open circuit with such high resistance measured or is 3500ohms normal. And if pump is bad, and i am unable to manipulate the codes set by doing these circuit bypasses, will I also need a module?
I can't do much tonight for you but certainly will offer any assistance needed tomorrow.
As there are no vehicle-specific replies yet, I will take a shot at it as a generic BLDC motor. 3500 Ohms is very high. The motor needs to be replaced. To trip the circuit protection in the module and get P208D, the jumper wire has to be beefy and needs to have good contact with the connector. So double-check that. Another way to test the module is to disconnect the motor and put an
Hi Maynard, I'm not familiar with this setup but I have done some 3-phase motor testing in hybrids. I use a milliohm meter and measure from phase to phase with the motor unplugged. I look for evenness between the phases. It appears that the phase B and C are shorted together. It's strange that your getting a code for phase A though and you can't manipulate the codes. It's possible both the
I don't have service information available to me at this moment, but just judging off the code description of circuit high I would want to verify wiring integrity of Phase A as well as the modules ability to sense and respond to the change of state. An easy test would be to use a test light (or resistor) hooked to ground and then test Phase A wire while monitoring the appropriate Data PID (if
Hi Maynard: Just something to add to what Dmitriy mentioned: You can take 2 channels of your scope, use 1 channel for an amp clamp and the other to monitor the switched circuit voltage. (Obviously, if you have no amps, you have no work. You'll have to substitute a load.) But what is the voltage doing? Since I don't know this particular system, I'm going to assume that it is low side controlled…
Thank you everyone. There has been some very good suggestions in the responses. I appreciate everyone reading. So.... yes in order to run the pump with scantool command the original code has to be cleared first, test is aborted due to codes set etc. So in order to get some action i believe that is why SI states to connect another phase to phaseA then watch if one code goes inactive and another
Appreciate the update. I'm looking forward to your follow up, and I am quite sure Dmitriy will be curious as to your results as well. If time and tooling allow, I would love to see you follow Dmitriy and Anthony's advice, after installation of the new pump, and "put an oscilloscope on Phases A, B, and C, and measure relative to the chassis ground" and/or "take 2 channels of your scope, use 1
Do you have any freeze frame for the code? This might help with your diagnosis.
Maynard, Any updates on this vehicle? I know you had mentioned getting a pump. I'm curious as to what the outcome was.
Mr. Chris So i really want to know about this too. However, unfortunately the client wanted a second opinion and it is away from us right now. I suppose we will hear back but as far as more testing, it cant happen right now. The second opinion is suggesting just a module ..... maybe that will do it..? Thank you for your interest
No need for the mister, I'm about three pay grades and a lot of class below the mister title. I appreciate it nonetheless. Just because the vehicle is gone for now doesn't mean this is all for nothing. Maybe there is still a chance to learn something here. As Michael said above, freeze frame data from the code would be one insight, if you happen to have that saved. My gut feeling, without
I dont have the freeze frame. I did a load test on the harness through the 3 circuits, they all handled a sealed beam headlight current. I did test the voltage coming out of the module on phase A, 3.5 v open circuit. Phase b and c 0v open circuit. Connect A and B this drops voltage from 3.5 to 2.5v same when A and C are connected. I did not test it with scope at key on event. I grounded phase A
Maynard, if you are confident about those 3500 Ohm Phase A-B, A-C measurements, I see no way the pump can be good. The doser module does not behave OK either, though. It’s possible a bad module cooked the motor, and now both are bad.
Hi Maynard, is the Pump controlled by a comm network such as Can? You have ruled out wiring, but I have a question about the Pump. Does service info give you a resistance spec for the Motor? Reason I ask is because sometimes these pumps have electronics built into them and this could be effecting your resistance readings. Also the reason I brought up the question about if the pump is controlled
Hi Michael That is a big part of the trouble here, we dont have a resistance spec and the schematic shows the 3 phase circuits are directly hardwired into the pump phases. So what exactly is inside the pump and what actually triggers the codes is a bit of mystery. What would be helpful is to have another known good vehicle parked right next to it to get some readings from it. Thanks for your
Can you show the schematic?
Yes! sorry I should have done that first time around. I attached it to original post
Do you have a scope Maynard?
Yes sir we have a scope, the truck is gone now unfortunately
Well that's too bad, what did the customer decide to do?
They wanted a second opinion, the second opinion says replace module. So from there i am not yet sure what they will do. I did find a bit more description on the motor. This is from Chrysler SI states module provides 12V and ground to the motor then also a pulse width modulated signal to control the speed. ..? how should we interpret that you think? Thanks for your interest
Maynard, PWM (pulse width modulation) is a means of controlling something, a motor in this case, using On/Off of a voltage supply at varying rates (duty cycle). I will use a blower motor as an example, a salt spreader motor would be another than you've probably dealt with being in the great north. So in previous times you would have a blower motor that had high speed with straight 12v supply…
And from what we know so far.... would we maybe suspect phase A to be pulse modulated and phase B and C would have steady powerand ground? At that rate if b and c had such low resisance near 0 ohms that the motor might be okay...? Lol. I will try to update when i hear more back
Maynard, the answer is that each phase sequentially becomes 12V, 0V, and open, and the timing of those is what pushes the rotor in the right direction. There is a full description of what is happening, but it might be geared towards engineers too much? digikey.ca/en/articles/te… SI's description "module provides 12V and ground to the motor then also a pulse width modulated
Dmitriy beat me to it so I'll condense mine. 3 phase brushless dc motors (bldc) work by switching the phases on and off at specific times. When they are used with the proper motor controller (your SCR control module in this case) they should be able to be controlled directionally. This specific pump appears to use back EMF to sense position/direction but that's a discussion for another time. I
I just saw the post about the brushless motors. Interesting. (I didn't see a way to delete my post, hence an edit.) Guido
Me too, I have never encountered a 3 phase bldc motor problem with Cummins. Eeverything I have encountered so far is the brushless pulse width modulated Pumps on the midrange Engines.
An update to this post, A new module was installed, this did not get system to work. Then a new pump was installed and module programmed. This restored functionality. So,,, I dont know this for certain but am thinking if only a new pump would have been installed and both PCM and DCM would have been reflashed the system may have regained functionality without replacing the DCM.
Appreciate the update Maynard. Such is the nature of our industry that sometimes we don't get the chance to have a clean cut ending. We can perform thought experiments after the fact or, as I do, re-examine the data we have collected while considering the fix and see if it makes sense. Every job is a learning experience in some way, shape, or form. I'm glad to hear that there was at least a