#transmission
30 posts in Car Diagnostics blog about "transmission" — OBD-II diagnostics, DTC codes, repair. ← All posts
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P0703 and P0706: brake switch B and transmission range sensor
Two codes that both mean the gearbox does not know what you asked it to do. One comes from the pedal, the other from the selector.
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P0710 to P0713: transmission fluid temperature sensor circuit
Fluid temperature decides when the torque converter locks up and when the gearbox protects itself. A wrong reading changes how the car drives before it sets a code.
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P0716 and P0717: input/turbine speed sensor circuit and no signal
The gearbox compares input speed with output speed to know whether a clutch is holding. Lose that input and it cannot tell slip from a gear change.
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P0731 to P0736: incorrect gear ratio, gear by gear
Which gear the code names tells you which clutch or band is slipping. That is a genuinely useful piece of information before anyone opens the gearbox.
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P0745 to P0747: pressure control solenoid A faults
Line pressure decides whether a clutch holds or slips. This solenoid sets it, and it is dramatically cheaper than the rebuild people are quoted instead.
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P0751 and P0752: shift solenoid A performance and stuck off
A shift solenoid that is electrically perfect can still be mechanically stuck. Knowing which of the two you have decides whether the pan comes off.
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P0760 and P0761: shift solenoid C circuit and performance
A third shift solenoid means a gearbox with more ratios, and more ways for one stuck valve to remove several gears at once.
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P0755 to P0757: shift solenoid B circuit and performance
Solenoid B fails the same way as A, but the gears it removes are different — and that difference is what makes the code worth reading carefully.
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P0776 and P0778: pressure control solenoid B performance and electrical
A second pressure control solenoid usually manages the torque converter clutch or a specific clutch pack. Its failure produces shudder rather than slip.
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P0842 and P0843: transmission fluid pressure sensor A circuit
Before believing the gearbox has lost pressure, check the instrument that measured it. A faulty sensor turns a healthy transmission into an expensive quote.
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P0868: transmission fluid pressure low and the limp mode behind it
The gearbox measured its own pressure and found it insufficient. That is a protective code — it appears before the damage, not after it.
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P0882 and P0883: TCM power input signal low and high
The transmission module is reporting a supply problem. Every harsh shift and every limp mode that follows is a symptom, not a separate fault.
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P0894: transmission component slipping — measured, not guessed
The module compared what the gearbox should be doing with what it is doing, and named the difference. This is the code that precedes the expensive conversation.
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Manual gearbox will not go into gear: clutch or linkage
Whether it refuses every gear or only one narrows the cause immediately. A clutch that will not release and a stretched selector cable feel similar and cost very differently.
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Clunk when shifting into drive: mounts, backlash or gearbox
Some clunk is normal — drivetrain slack has to be taken up somewhere. Telling normal slack from a worn mount or a failing gearbox comes down to timing and repeatability.
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Automatic gearbox slipping: what to check before a rebuild quote
Revs rise, speed does not. Before accepting a four-figure quote, three checks separate a fluid problem from a worn clutch pack — and they are all cheap.
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Nissan X-Trail: OBD diagnostics and the CVT question
The engine is rarely the problem on an X-Trail. The continuously variable transmission is where the risk and the money are, and it announces itself early if you know what to log.
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P0700: the transmission code that is only a pointer
P0700 is not a fault. It is the engine ECU telling you the transmission module has stored something, and that you are reading the wrong module.
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P0705: transmission range sensor and the car that starts in any gear
The range sensor tells the car which gear you selected. When it fails, the symptoms range from a reverse light that never works to an engine that will start in Drive.
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P0715: input/turbine speed sensor faults and erratic shifting
The turbine speed sensor is how the gearbox knows what the torque converter is doing. Lose it and shift quality collapses, but the cause is often a magnet covered in swarf rather than a failed sensor.
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P0730: incorrect gear ratio — slipping clutches or a lying sensor
P0730 means the gearbox commanded a gear and measured a different ratio. Whether that is mechanical slip or a bad speed signal decides between a fluid service and a rebuild.
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P0740 and P0741: torque converter clutch circuit and stuck-off faults
The converter clutch is what turns a slushbox into a direct drive at cruise. When it stops locking, fuel consumption rises, the gearbox runs hot and these two codes appear.
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P0750-P0758: shift solenoid codes and what they really mean
Shift solenoid codes name a letter, not a gear. Understanding what each solenoid controls and why they stick turns a scary transmission code into a manageable repair.
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Transmission overheating warning: causes and immediate actions
Heat is what kills automatic gearboxes, and the relationship is brutal: every 10 °C above normal roughly halves fluid life. What you do in the next five minutes matters.
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Whining noise when accelerating: belt, pump or gearbox?
Whether the pitch follows engine speed or road speed is the entire diagnosis. One test in a car park separates a cheap belt from an expensive differential.
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Differentials and transfer cases: the units people remember after the whine
Axle and transfer case oil has a schedule that quietly gets skipped. Wear signs and why mismatched tyres destroy four-wheel drive.
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Automatic transmission fluid: "filled for life" and the other myths
A "lifetime fill" means the life the manufacturer assumed, not yours. When to change it, how a partial change differs from a full one, and why the fear is misplaced.
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Clutch nearing the end: the signs, the checks, and the driving habits that cause it
A clutch rarely dies suddenly. The early signs, two checks that need no ramp, the difference between manual and dual-clutch units, and what diagnostics sees.
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Towing a car with an automatic: why "just a hundred metres" sometimes costs a gearbox
On a manual, towing is a question of having a rope. On an automatic it is a question of the lubrication pump, which only runs with the engine running. The limits and the safe options.
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Transmission will not shift: limp mode, fluid, and what to read before the workshop
The automatic is stuck in third, the manual will not select a gear, the dual-clutch judders. Diagnosis by transmission type, why fluid is usually to blame, and what to read before clearing anything.