trans limp mode help

[Busadave]

5.9 Cummins 

47RE

No previous issues. Went out one morning, started the truck and trans was in 3rd gear limp mode.  

No low gear, No OD

So I jumped the gun without diagnosing and just went ahead and Replaced the typical governor pressure sensor and transducer,  however issue remained the same. 

Started testing wires and found pin#1 on transmission connector does not have 12v with engine running like it should. 

Thought problem was PCM. So I sent it out to be rebuilt and they tested it and said it was good and had no issues when testing it.  I Re-installed PCM and issue remained the same. 

 

I tried a jumper wire in the distribution box where the trans relay goes.  With this installed I of course get the 12v to the trans connector pin#1 and have gears  1,2,3 and TC lockup. But no OD as the PCM isn’t commanding it I presume. 

 

I found testing the trans relay connector side of the distribution box that the powers and ground are all there to actuate the relay without the relay installed. However as soon as the relay is installed, the PCM kills the ground side of the relay.  this happens both when the transmission connector is plugged in at the trans or unplugged at the trans. This leads me to believe it is not an internal trans issue. But the PCM is seeing something it doesn’t like and going into limp mode.  I just can’t seem to find what?

I haven’t been able to find any obvious wiring defects. Found a couple possible defects but repaired them with no change to the issue. 

Tried another known good PCM from a friend’s truck and issue remained the same. 
After doing some more reading today, I’m thinking another possible cause of this could be the ess signal coming from the ecm to the pcm. But not sure how to test this?

you fellas have any other ideas?

Edited March 17 by Busadave

[Mopar1973Man]

Do you have a PCM noise filter installed?

[Busadave]

 

3 minutes ago, Mopar1973Man said:

Do you have a PCM noise filter installed?

no noise filter 

[IBMobile]

Have you seen this in the FSM?

 

NO LOW GEAR (MOVES IN 2ND OR 3RD GEAR ONLY) 1. Governor Circuit Electrical Fault. 1. Test with DRBT scan tool and repair as required. 2. Valve Body Malfunction. 2. Remove, clean and inspect. Look for sticking 1-2 shift valve, 2-3 shift valve, governor plug or broken springs. 3. Front Servo Piston Cocked in Bore. 3. Inspect servo and repair as required. 4. Front Band Linkage Malfunction 4. Inspect linkage and look for bind in linkage

[Busadave]

7 hours ago, IBMobile said:

Have you seen this in the FSM?

 

NO LOW GEAR (MOVES IN 2ND OR 3RD GEAR ONLY) 1. Governor Circuit Electrical Fault. 1. Test with DRBT scan tool and repair as required. 2. Valve Body Malfunction. 2. Remove, clean and inspect. Look for sticking 1-2 shift valve, 2-3 shift valve, governor plug or broken springs. 3. Front Servo Piston Cocked in Bore. 3. Inspect servo and repair as required. 4. Front Band Linkage Malfunction 4. Inspect linkage and look for bind in linkage

I did see that.  I do have the 5v on the orange wire.   the other possible issues listed there should out of the loop as it’s doing it without the transmission plug connected. Ive tested all the wires in that circuit for shorts to ground and shorts to hot and not found anything that would cause this.  

[Great work!]

Any codes?

 

Is charging system working (NA for external regulator conversions). Is AC clutch working, if worked previously?

 

Swap relay with another.

 

Starter only works in park and neutral and not in drive?

 

Output speed sensor causes stuck in first symptoms not usually limp.

 

TC solenoid and OD solenoid should have good resistance readings both are similar. 

 

Speedometer works?

 

Internal temperature sensor resistance reading?

 

Clean re-seat all connectors above engine by brake booster.

[Busadave]

27 minutes ago, Great work! said:

Any codes?

 

Is charging system working (NA for external regulator conversions). Is AC clutch working, if worked previously?

 

Swap relay with another.

 

Starter only works in park and neutral and not in drive?

 

Output speed sensor causes stuck in first symptoms not usually limp.

 

TC solenoid and OD solenoid should have good resistance readings both are similar. 

 

Speedometer works?

 

Internal temperature sensor resistance reading?

 

Clean re-seat all connectors above engine by brake booster.

There are no codes with my OBDII scanner

I swapped that relay with the horn relay. Horn still worked and trans still did not. 

speedo works.  Tach works

haven’t checked the internal temp sensor.  I will have to look into that. 

I did disconnect and clean the connections on the firewall where the harnesses meet. 
the TC and OD are out of the loop with the trans connector disconnected so that shouldn’t be the cause of no 12v on the red wire pin 1 from the trans relay. 

[Great work!]

Try tweeking the relay pins and sockets. Maybe just bad connections 

[Busadave]

8 minutes ago, Great work! said:

Try tweeking the relay pins and sockets. Maybe just bad connections 

It’s not that. The pcm is killing the ground for the relay as soon as it’s plugged in. I verified this at the pcm by probing the wire that supplies ground to the relay. It has continuity to ground, then as soon as the relay is plugged in the pcm kills it. 

[IBMobile]

How about the two ground wires for the PCM.   They are the black/tan 14gauge wires at PCM terminals C1 #31 and #32.  They go to splice S126 before going to the right side battery.  Here is a link to what I did to improve the grounding continuity.

 

https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation_50/51_engine/electrical/pcm-ground-splice-repair-r675/?tab=comments#comment-115

[Busadave]

On 3/18/2024 at 4:13 PM, IBMobile said:

How about the two ground wires for the PCM.   They are the black/tan 14gauge wires at PCM terminals C1 #31 and #32.  They go to splice S126 before going to the right side battery.  Here is a link to what I did to improve the grounding continuity.

 

https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation_50/51_engine/electrical/pcm-ground-splice-repair-r675/?tab=comments#comment-115

Grounds are good. I went over the complete pcm/trans harness with it removed from the truck.
 Do you happen to know if the red wire (pin 1) at the 8pin transmission connector would have the 12v with the connector unplugged at the transmission with the engine on?  Or does the PCM need to see the gov pressure, trans temp, etc that also comes through that connector.  
 

[IBMobile]

The 12 volts comes from the transmission relay and is used to power the torque convertor solenoid, overdrive solenoid and the variable force solenoid (governor pressure solenoid).  With the 8pin transmission connector unplugged The PCM would not get a transmission temperature signal or a governor pressure signal.

 

[Great work!]

Intentionally cause a trouble code for the PCM by disconnecting the transmission plug or the battery temperature sensor. That way you can make sure you are getting codes. Limp mode should cause a code. Also cause a fault with the ECM by disconnecting the MAP or APPS that will cause a companion code.

 

Check your OD solenoid resistance. You said earlier that it didn't work when you bypassed the relay.

[Busadave]

8 hours ago, Great work! said:

Intentionally cause a trouble code for the PCM by disconnecting the transmission plug or the battery temperature sensor. That way you can make sure you are getting codes. Limp mode should cause a code. Also cause a fault with the ECM by disconnecting the MAP or APPS that will cause a companion code.

 

Check your OD solenoid resistance. You said earlier that it didn't work when you bypassed the relay.

I had no codes, but I just have a standard OBD2 scanner.  From what I’ve read it may or may not pick those up. 
I tried to ohm the pins on the trans side of the connector but couldn’t see too well with the mirror.  Probably should just plug the connector in and probe the wires.  
im going to drop the pan when the rain stops and just go ahead and replace the OD/TCC solenoid and harness as I believe I’ve ruled out damm near everything else.  
thank you for your help. 

[Busadave]

On 4/3/2024 at 5:12 AM, Busadave said:

I had no codes, but I just have a standard OBD2 scanner.  From what I’ve read it may or may not pick those up. 
I tried to ohm the pins on the trans side of the connector but couldn’t see too well with the mirror.  Probably should just plug the connector in and probe the wires.  
im going to drop the pan when the rain stops and just go ahead and replace the OD/TCC solenoid and harness as I believe I’ve ruled out damm near everything else.  
thank you for your help. 

Looks like I’ve been able to finally find the issue. There is a failure in the OD solenoid/ wiring.  Between pins 5 and 6 there should be 28-68 ohms.  I have OL.  All other resistances are within spec.  New solenoid assembly will be here tomorrow.  
I should have found this earlier when I was doing all my diagnostics but couldn’t see the PIN numbers on the trans side plug with my mirror.  Should have used my head and just plugged in the connector and probed the wires.  But I got sidetracked with the relay circuit.  It didn’t make sense that as soon as the relay was installed the PCM killed the ground whether the trans plug was connected or not.  I guess the little current draw from the relay was enough for the pcm to kick to limp mode because it wasn’t reading from the trans.  Just didn’t make sense that the circuit had all the hots and ground without the relay plugged in. 

Edited April 4 by Busadave