TCM codes, including "implausible data" code?

2008 DODGE CALIBER
118,000 MILES • 2.0L • 4 CYL • 2WD • AUTOMATIC
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MIKEHE
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Car has TCM codes, including "implausible data" code. Upon inspection using my Autel scanner, the engine speed reported by the TCM is 3300 with the engine off. This is true through two separate TCM units. I have reset and re-initialized both units, both with no change. The procedure cannot be performed because the "engine is on", which it is not. What feeds the TCM the engine speed information? Does it come from a sensor, but through the PCM? Or directly from a sensor? I don't want to condemn or pay to re-flash the TCM if that won't solve the problem. The fact that the information is consistent (wrong) across two separate units leads me to believe there is something else to blame.
May 8, 2023 at 1:48 PM
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STRAILER
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It looks like the engine input speed for the TCM is handled by the input shaft speed sensor. here are the wiring diagrams for the transmission and TCM so you can see how the system works and the location of the sensor as well. Check out the images (below). Please let us know what happens.
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May 8, 2023 at 6:19 PM
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MIKEHE
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Replaced the input speed sensor, no change. The engine speed shows 3,488 RPMs with the engine off still. In fact, it shows that even with both sensors unplugged. I'm not sure the TCM engine speed comes from either of these sensors. The PCM engine speed reading is accurate (0RPM) with the sensors plugged in or unplugged. Could it come from a cam or crank sensor? Does this vehicle have those?
May 9, 2023 at 6:54 PM
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STRAILER
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Yes, you have both cam and crankshaft sensors. I would try a rebuilt TCM.
May 10, 2023 at 11:12 AM
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MIKEHE
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That has already been done. The same incorrect information shows up in both the old and new TCM. I found a copy of the FSM for this vehicle, and the crank sensor signal goes straight to the PCM, then engine speed is transmitted to the TCM via the CAN system. So, I believe the issue is either within the PCM or some wiring is damaged. The strange thing I noticed last night is that the engine speed signal is accurate during cranking and for a few seconds after startup, then goes right back to 3,488 RPMs and doesn't change after those few seconds.
May 10, 2023 at 11:28 AM
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STRAILER
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Yep, it sure sounds like the PCM is bad, I would get a rebuilt unit by searching google or eBay. Here is the location of the PCM and how to change it out, also when the electrical connectors are disconnected check the terminals for corrosion. Check out the images (below). Please let us know what happens.
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May 11, 2023 at 9:07 AM