Attention: TDR Forum Junkies 
I had a problem with the cruise control in my 2004.5 Dodge and I wanted to share what I found.
Problem: The cruise control would work for awhile and then would disengage. This seemed to happen when starting up a hill when more cruise control servo effort was needed. The "Cruise" light in the display was still on but the cruise control would not re-engage with a press of the resume button. Turning the Cruise Control master off and back on had no effect, it still would not re-engage. However, after a stop with key off, the cruise would work again until dropping off as described above.
Solution:
Found that the vacuum pump was not working. Used an aftermarket replacement pump, Dorman 904-214.
Also found a leak in the hard vacuum tubing due to wear. The constant leak may have led to the eventual pump failure.
Diagnostic notes: After much research in the FSM and a bit online, I began troubleshooting.
1. Checked the vacuum lines and found a point where the thin plastic line had worn through where it was rubbing on the cable from the cruise control servo near where the plastic line departed from the cable and headed to the firewall. The line was brittle and a section broke out when handled. Did a quick test on the line running toward the servo with a mityvac to make sure the diaphragm in the servo was OK.
2. The vacuum pump was not running with key on (run position) as indicated in the manual. Checked the power at the connector that plugs in to the vacuum pump. The FSM has a good simple diagram of the wiring circuit and the pinout of the connector. Supplied power was good. (vacuum line was not repaired at this point so pump should have run)
3. Connected the vacuum pump to 12v via the pins in the connector recess on the pump but it did not run indicating a bad pump.
4. Just to cover the bases, after repairing the broken line I disconnected the vacuum line at the pump to check the whole of the vacuum lines/system from the source with the mityvac and it held vacuum.
Some things I learned: (May be common knowledge)
- The vacuum system only serves the cruise control. The motors/servos that control the HVAC in the cab appear to be electric. (I looked up the damper motor as listed in the parts manual and the picture on the Mopar parts site clearly showed an electric connection)
- The vacuum pump is located next to the coolant tank near the passenger firewall corner. The cruise control servo is located under the driver battery. The hard vacuum line runs between the two along the upper firewall.
- The FSM states that a Ram with the diesel engine does not have a vacuum reservoir but this was not so in my case. The vacuum reservoir is located (and visible) under the cowl vents at the base of the windshield and supplied by a tee in the vacuum line running across the upper firewall. The FSM calls it a vacuum reservoir but an online Mopar parts source calls it a vacuum dryer.
- The plastic vacuum lines appear to be 5/32" OD. (also called emission tubing)
Kevin
Problem: The cruise control would work for awhile and then would disengage. This seemed to happen when starting up a hill when more cruise control servo effort was needed. The "Cruise" light in the display was still on but the cruise control would not re-engage with a press of the resume button. Turning the Cruise Control master off and back on had no effect, it still would not re-engage. However, after a stop with key off, the cruise would work again until dropping off as described above.
Solution:
Found that the vacuum pump was not working. Used an aftermarket replacement pump, Dorman 904-214.
Also found a leak in the hard vacuum tubing due to wear. The constant leak may have led to the eventual pump failure.
Diagnostic notes: After much research in the FSM and a bit online, I began troubleshooting.
1. Checked the vacuum lines and found a point where the thin plastic line had worn through where it was rubbing on the cable from the cruise control servo near where the plastic line departed from the cable and headed to the firewall. The line was brittle and a section broke out when handled. Did a quick test on the line running toward the servo with a mityvac to make sure the diaphragm in the servo was OK.
2. The vacuum pump was not running with key on (run position) as indicated in the manual. Checked the power at the connector that plugs in to the vacuum pump. The FSM has a good simple diagram of the wiring circuit and the pinout of the connector. Supplied power was good. (vacuum line was not repaired at this point so pump should have run)
3. Connected the vacuum pump to 12v via the pins in the connector recess on the pump but it did not run indicating a bad pump.
4. Just to cover the bases, after repairing the broken line I disconnected the vacuum line at the pump to check the whole of the vacuum lines/system from the source with the mityvac and it held vacuum.
Some things I learned: (May be common knowledge)
- The vacuum system only serves the cruise control. The motors/servos that control the HVAC in the cab appear to be electric. (I looked up the damper motor as listed in the parts manual and the picture on the Mopar parts site clearly showed an electric connection)
- The vacuum pump is located next to the coolant tank near the passenger firewall corner. The cruise control servo is located under the driver battery. The hard vacuum line runs between the two along the upper firewall.
- The FSM states that a Ram with the diesel engine does not have a vacuum reservoir but this was not so in my case. The vacuum reservoir is located (and visible) under the cowl vents at the base of the windshield and supplied by a tee in the vacuum line running across the upper firewall. The FSM calls it a vacuum reservoir but an online Mopar parts source calls it a vacuum dryer.
- The plastic vacuum lines appear to be 5/32" OD. (also called emission tubing)
Kevin
