Delivering the Goods - June - 2021

Challenging Times – A Dodge Challenger with an 845RE in Failsafe

A customer came into the shop with a 2016 Dodge Challenger with a 3.6L motor and an 845RE transmission with a no-shifting complaint. He owned the vehicle from new and experienced a no-start condition one morning. Being a do-it-yourself kind of person, he jump-started his car a few times and eventually replaced the battery. After he replaced the battery, he noticed that the car was not shifting but had forward and reverse movement. The check engine light was on as well. There were no driveability issues or codes before jump-starting the car.

Just the Facts, Sir!

Anytime a DIY customer comes in and says, “I didn’t do anything,” I always worry about worse-case scenarios and begin to formulate questions. I asked this customer whether he accidentally hooked up the jumper cables wrong or saw sparks jumping off the battery terminals or if the ignition was left on while jumping the vehicle or changing the battery. He answered no to all. Then, I turned up the intensity of questioning! Mind you, all of this was done in good humor but with an exerted effort to get the truth. I asked if he had any recent work performed on the vehicle and if there was any aftermarket tuning performed on the vehicle? He answered no to everything and looked genuinely distraught. With those facts in place, we were able to start an honest diagnosis!

The Initial Inspection

The customer’s complaint was verified with a check engine light illuminated. Unfortunately, with most late-model vehicles, it’s hard to tell if the light at the end of the tunnel is a way out or a train! A scan revealed a code P1DD2-00 (Torque Request Signal from TCM Denied) and P0335 (Crankshaft Position Sensor Circuit). Both codes showed up in the PCM. The codes were recorded and cleared. The P1DD2 code was the only one that returned, and the transmission remained in limp mode. With this information in hand, we prepared the customer for a worst-case scenario and secured 2 hours of diagnostic time.

First, we have to interpret what the code means before we can proceed. According to OEM resources, this is a CAN Signal Monitoring code described as follows:

“If the sending control unit does not have valid information to send, it may send a defined failure value indicating an invalid signal. Incoming signals with a defined failure value are monitored for signal validity. For some outgoing signals, the Transmission Control Module (TCM) reads its own signal back from the CAN bus to monitor the signal transmission for disturbances.”

In other words, if the TCM receives data from other modules that might not make sense, it uses what it is programmed to expect for comparison. If the incoming data is not within an acceptable value, the data is rejected and sets the code. Also, if the values stored by the TCM are incorrect based on sensor data, the code will be set.

For example, if the driver is operating the vehicle from a stop under heavy acceleration, the TPS may show a value of 70%. If, at the same time, the MAF value shows a maximum of 10 g/sec., the TCM will reject this reading based on the expectation of a much higher MAF reading under heavy demand.

This code can be set providing vehicle voltage is within a calibrated range, and no Controller Area Network (CAN) bus monitoring Diagnostic Trouble Codes (DTCs) set nor any CAN bus message monitoring DTCs are set. The following additional conditions must also be present for the code to set:

  • A fault is detected if any of the following conditions occur:
  • The incoming signal is set to a default value indicating an invalid signal.
  • The incoming signal has a validity bit set in the message indicating an invalid signal.
  • The value of the outgoing signal is not equal to the feedback signal, which is immediately read back by the TCM.

When the code is present, the following default action will be taken by the powertrain management programming:

  • Malfunction Indicator Lamp (MIL) is illuminated on the first trip that the diagnostic fails.
  • The Transmission will be placed into Limp-in mode.
  • The Transmission Control Module (TCM) will not request any positive torque interventions from the Powertrain Control Module (PCM) via CAN.
  • The TCM will limit the current to the Torque Converter Clutch (TCC) solenoid to 50mA. The TCC will be open.
  • Maximum system hydraulic pressure will be limited.
  • Shift adaptation functions will be disabled.
  • The Start/Stop feature (if equipped) will be disabled.

The factory diagnostic information directed us to look for codes in the BCM, PCM, and TCM. If no codes were found in these modules, the TCM might be faulty.

Testing and Diagnosis

Once preliminary checks were performed and the battery and charging system was verified to be good, we followed the P1DD2 code diagnostic tree. Since there were not many options for the cause based on prior vehicle operating conditions, we started with sensor data for clues of what could be happening. We monitored crank and cam sensor data hoping to find glitches or issues to no avail.

Next, we decided to enlist the help of the OEM wiTECH2 scan tool. Our local programmer assisted us with this task (for a fee, of course). The wiTECH2 was able to verify that there were no wiring faults between modules and that all modules, including the TCM, were capable of communicating. It showed the same diagnostic trouble code P1DD2 and the TCM in failsafe mode.

At this point, we decided to program the PCM and TCM to make sure the current level software was not corrupted by a loss of power or a possible power surge. After programming, nothing changed. At this point, we were worried about the TCM being bad.

Before going further, Scotty, the diagnostician, decided to look into the possibility of the P0335 code being an issue even though the code never returned. We agreed to purchase a new sensor and check the connector and wiring. Everything looked so clean and new (figure 1)! There was a valence pan underneath the engine protecting the sensor and wiring in that area too. We changed the sensor and then checked and cleaned the terminals. Using the scan tool, we performed the Cam/Crank Relearn procedure. Our tests showed the same results.

Being the most curious of all diagnosticians I know, Scotty decided to take another look. He unwrapped the new-looking wiring loom near the crank sensor (figure 2). Much to our surprise, he found a wire that was barely making contact and fell apart when he handled it! There was no evidence of tampering, damage, or wear in that area. He repaired the wire, cleared the code, and the transmission was no longer in limp mode!

He drove the car around for a half-hour to verify everything was okay. There were no problems or issues. I drove it with no issues as well.

Extra Attention to Detail

In retrospect, FCA products can be reluctant to reset a trouble code. When sensor codes are found in constant memory, always check for connector and/or wiring issues that could create intermittent faults that are hard to trace. By unplugging and reconnecting sensors, you may solve the problem. Always use pin cavity size checking and cleaning tools (figure 3). Take a trip to your local auto recycling yard and get some old connectors to make your own pin-sizing tools. Extract male and female connector ends for terminal test tools.

Late-model vehicles give us more diagnostic information than earlier model vehicles ever could. With that information comes a learning curve for us to understand and interpret what these new codes mean and where to look for the problems. While more codes were meant to simplify our diagnostic process, becoming familiar with them proves to give us challenging times ahead!

A special thanks to Scott “Scotty” Edwards at Gearbox Industries, Mesa, AZ, for sharing the diagnostic process!