Guide step
Start by respecting what each code is actually accusing
P0700 is not the diagnosis; it is the engine module waving a flag that the transmission controller has its own story to tell. P0715, P0716, P0717, P0718, P0720, P0722, and the engine-speed-input bridge codes P0725 through P0728 are the data-input side of that story because they attack the speed information the TCM needs for shift timing and ratio math. P0730 and the gear-specific ratio codes P0731 through P0736 are different. Shift-solenoid E codes P0770 through P0774 add another layer by attacking the hydraulic command path instead of the ratio math itself. They say the commanded gear and the measured result no longer agree. That can happen because the data is wrong, but it can also happen because the transmission really is slipping.
Guide step
Do not confuse transmission limp mode with generic engine reduced power
Drivers often call both problems limp mode. The useful split is simple: if the engine itself is throttle-limited but the transmission still shifts normally, stay in the reduced-power branch. If the transmission is stuck in one gear, bangs shifts, or refuses upshift, stay in the transmission branch even if acceleration feels weak.
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What points toward bad transmission data first
If the complaint arrives with sudden limp mode, fixed-gear operation, harsh shifts right away, and one or more clear speed-sensor codes, start by proving the TCM can actually see believable input and output speed. A missing or irrational speed signal can make a healthy transmission act broken because the controller loses the references it needs to apply and verify shifts. Connector contamination at the case, internal harness damage, and failed speed sensors often live here.
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What points toward real slip instead
If live data shows believable speed signals but the ratio still goes wrong under load, the mechanical and hydraulic branch climbs fast. Burnt fluid, flare on the shift, delayed engagement, and repeat ratio faults after speed-sensor checks make clutch leakage, line-pressure weakness, valve-body trouble, or converter problems much more believable. P0730 is especially important because it sits right at that split between false math and true transmission slip, while P0731 through P0736 tell you which gear or reverse range is failing that test.
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Why P0741 belongs in the same conversation
P0741 is not a gear-ratio code, but it belongs nearby because converter lockup changes how the TCM expects slip to behave at cruise. If the converter clutch will not apply, highway RPM stays high and heat rises. Sometimes P0741 is a separate lockup-control problem. Other times it shows up next to speed-sensor or ratio issues that are already confusing the controller. That is why lockup data should be viewed in the same session as input-speed and output-speed data.
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A practical diagnostic order that saves money
First, read the transmission module directly and capture freeze-frame. Second, compare engine RPM, input speed, output speed, commanded gear, and actual converter slip before clearing anything. Third, inspect the case connector and harness because fluid intrusion there can fake expensive transmission failure. Fourth, check fluid condition and signs of overheating. Fifth, if the data is credible and the ratio is still wrong, move toward pressure, valve-body, converter, or internal-clutch diagnosis with confidence instead of guesswork.
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The real-world takeaway
Transmission complaints get expensive when shops skip the data split. If the TCM is blind, fix the blindness first. If the TCM can see clearly and still says the ratio is wrong, believe it and inspect the mechanical side. That simple discipline is the difference between a sensor-and-connector repair and an honest conversation about internal transmission failure.