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Nixing NAG 1 problems

Learn how to tackle some issues you may see with the New Automatic Gearbox Generation One
Monday, May 2, 2016 - 06:00
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In this Powertrain Pro section, we have written several articles about the NAG 1 five-speed automatic transmission used in Dodge, Chrysler and Jeep vehicles. It comes in both two-wheel drive and four-wheel drive configurations and may also be referred to as the WA580, W5A580, 5G-Tronic or 722.6 transmission. This article will continue with some additional issues that may show up in your shop.

A good friend and meticulous rebuilder, Dale Desveaux, owns and runs a shop in Napanee, Canada. He had a 2007 Chrysler 300 3.5L AWD vehicle with the NAG 1 unit come in to his shop. It exhibited a no up-shift condition and was unable to get speeds over 15 mph due to a loss of power from the engine.

He attached a scan tool and pulled the following codes:

  • P0501: Vehicle Speed Sensor 1 Performance — this code will set if multiple ABS wheel speed signals are invalid.
  • U140A: Implausible Right Front Wheel Speed Signal Received — readings compared at 25 mph
  • C101F: Right Front Wheel Speed Comparative Performance — different signal compared to others.
  • U140B: Implausible Left Rear Wheel Speed Signal Received — readings compared at 25 mph
  • C102A: Left Rear Wheel Speed Comparative Performance — different signal compared to others
  • C121A: Steering Angle Sensor Not Initialized — refer to C1231 Drive Test Steering Angle Sensor

This particular transmission does not utilize a traditional output speed sensor for a vehicle speed signal. The ABS system converts wheel speed signals (specifically the rear wheel speed signals) into a vehicle speed that is then broadcast over the network. The TCM receives this signal and utilizes this information for shift scheduling and gear ratio calculations, among other things. In fact, you can read “ISS Factor” (January 2014), which explains the calculations are made to determine gear ratios.

Since vehicle speed is coming from the rear wheel speed sensors, there are a number of items to consider if gear ratios are wrong. One obvious cause of incorrect gear ratios is a slipping transmission, and for many reasons of its own. But the not-so-obvious reasons, which can easily be overlooked, would be the use of a transmission with incorrect planetary gear ratios, the installation of an incorrect rear differential, a TCM misapplication or an incorrect pinion factor that was performed.

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