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R.E.D

No throttle .Please help.

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So while I was driving down the road the truck lost throttle.The pedal is completely dead along with the rpm gauge.Fault code is 6-4.I checked the connectors in the abs computer near the injector and the vecu in the cab.both show no corrosion. Also the triangle connector coming out the firewall.truck is idling higher than normal and the key won't shut the engine off until 15 to 20 second after the key is in the off position.Please advice on what further steps can be taken.truck is 98 ch 355hp

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From Mack Information System:

Blink code 6-4: J1939 serial data line

Failure Mode Identifier FMI: 8 (Abnormal)

Parameter Identification: S231

Message Identification MID: 128 (Abnormal), 142 (Abnormal)

Circuit Description: The V-MAC III system uses the J1939 data line to control communication between the Vehicle Electronic Control Unit (VECU), Engine Electronic Control Unit (EECU), Anti-lock Brake System Control Unit, Allison Transmission Control Unit, and accessory systems, depending on vehicle model and option content. The J1939 data line is an expandable data bus, allowing the addition of accessory control modules (Collision Avoidance, Traction Control, etc.) to be connected to the circuit. The J1939 data line is comprised of two circuits; the L circuit and the H circuit. The two wires are twisted together to prevent outside electrical noise from interfering with the data being carried by the L and H circuits. The V-MAC III system is designed to allow continued engine operation with the loss of the J1939 data line signal as long as the J1587 data line is still operational.

Code Setting Conditions: If either the Vehicle Electronic Control Unit (VECU) or the Engine Electronic Control Unit (EECU) loses communication on the J1939 data line for more than one half second, code 6-4 will set and the Electronic Malfunction Lamp (EML) will turn on. The fault will become inactive if communication resumes for at least on half second. When code 6-4 is active, engine speed will default to 900 RPM. If communication is lost on both the J1587 and J1939 data lines the engine will not run.

Fault code 6-4 will set for some mismatches of VECU and EECU software levels. Blink code 6-4 will also set while the VECU is in the programming mode for Customer Data, Fleet Data, or Mack Data. This code setting condition is normal and the code will become inactive after the ignition key is cycled.

Fault code 6-4 may log, without illuminating the Electronic Malfunction Lamp (EML), on vehicles equipped with Eaton/Bosch ABS/ATC module # 7MN54M2. This nuisance code will not affect the performance of the vehicle. When a vehicle equipped with this ABS/ATC module is being diagnosed for an inactive code 6-4, contact Mack Trucks Service Engineering.

Additional Symptoms:If communication is lost on just the J1939 line, the engine will only run at 900 RPM, no throttle response above 900 RPM

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So which one is the j1939.is it connected to the vecu?or the one next to it?there are two cables that are wrapped individually with some kinda foil on the inside of the plastic lining.they go to a 3 prong connector.are thy it?.is there an easier way to troubleshoot?thanks 

Red

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That is the shielded data link cables ,do not damage the foil as it cuts outside interference with the  data stream. . With out a scanner to check the balance of the system, I do not believe there is much you will be able to do aside from checking the connections.

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There are two communication systems in  your truck- the high speed j1939 system and the low speed j1587.  Look at it as J1939 is cable internet and j1587 is dial-up.  If you loose the j1939 to one of the ecu's--either the engine ecu or the vehicle ecu, you will get this fault.  If you loose both J1939 and J1587 then the engine will not start.

This is a PDF of the diagnostic flow chart for a 6-4 fault:

6-4 diagnostic flow chart.pdf

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Thanks for the great info fellas . found the problem to be one of the two sets of cable wrapped with foil . replace it and truck running like champ now.

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R.E.D. where did you find the j-1939 cable? My mack dealer says it's part of the whole dash harness which is hard to believe, its separate but plastic tied with the harness. I don't see why you can't purchase it separately

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Keep in mind any loss of voltage or ground to the control modules will log 6-4 also. The fault isn't always in the data link wiring. Fixed a  6-4 fault this week that was caused by engine harness wires rubbing on the block causing the engine module to lose power. 

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