OBD-II trouble code
P0735: Gear 5 Incorrect Ratio
Fifth is only commanded at sustained speed under light load, so a short test drive never enters it. A shop that reports no fault found after a lap around the block has tested every gear except the one this code is about.
Quick facts
- System
- Powertrain
- Category
- Transmission
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $3,400
- DIY difficulty
- Advanced DIY
Browse every code in P0700–P0799, or start from the full code library.
What does P0735 mean?
P0735 means the shaft speed relationship measured while fifth was commanded did not match what fifth should produce. Two things about this particular gear shape the entire diagnosis, and neither applies to the gears below it.
The first is that fifth is barely ever used. It is only commanded above a threshold road speed, with light throttle, once the transmission is warm and the vehicle is cruising steadily. That is a narrow set of conditions and none of them occur on a short drive. So a vehicle brought in with this code and given a ten-minute road test around local roads has been exercised in first through fourth and never once put into the gear the code concerns. The report that comes back — no fault found, code did not return — is accurate and completely uninformative. Reproducing this fault requires a sustained run at motorway speed with light throttle and the fluid fully up to temperature, with live data recorded. Two conditions on that test. The person driving should not be the person reading the scan tool — shaft speeds at motorway speed are a passenger's job, or a recording to review afterwards. And watch fluid temperature while you do it, because a slipping element at sustained speed is generating heat in the fluid that circulates through everything else; if the temperature climbs past normal, end the test rather than extending it to get a better trace. If nobody has done this at all, the fault has not been tested for.
The second is that a fifth-gear slip produces almost no drivability complaint. There is very little torque going through the transmission when the vehicle is cruising, so a marginal element that would slip obviously in first will slip almost imperceptibly here. What the driver notices, if they notice anything, is engine speed sitting a few hundred revolutions higher than it used to at the same motorway speed, and fuel economy quietly getting worse. Nothing bangs, nothing flares, nothing lurches. These codes are typically found during a scan for something else entirely. It is worth stating plainly that the absence of symptoms is not evidence of the absence of a problem, because that assumption is how a top-gear slip gets ignored until it becomes something larger.
There is a caveat that has to come before any parts are ordered. Fifth is not a consistent physical thing across designs the way the lower gears broadly are. It only exists on transmissions with five or more forward ratios, and on those it is produced in different ways — sometimes by an additional planetary set, sometimes by a second overdrive element, and on some designs by an add-on overdrive section behind the main gearbox. Confirm from service data how many forward gears your transmission actually has and which element serves fifth before anyone quotes for a part. A generic answer to this code does not exist.
The genuinely good news, and it is worth saying because transmission codes rarely carry any, is that a fault confined to fifth narrows the suspect list considerably rather than widening it. Every element used in first through fourth has just demonstrated that it works. Whatever has failed is either the element unique to fifth or the solenoid that commands it, and both of those are a smaller, shallower and cheaper proposition than a fault in a gear the vehicle depends on to move off. If the ratio codes had covered several gears the outlook would be much worse. Confined to top gear, this is the best version of this family of codes to get.
Common causes
- Fluid level low enough to aerate only at prolonged high-speed operation
- Shift solenoid for the fifth-gear circuit failing or responding slowly
- Seal or sealing ring leaking in the fifth-gear apply circuit at sustained temperature
- Wear in the overdrive element used only by fifth gear
- Valve-body wear affecting the circuit that is exercised least often
- Fluid degraded by heat on a vehicle that does mainly long highway journeys
- Output speed sensor inaccuracy that only becomes significant at high shaft speeds
- Adaptive shift values never correctly learned for a gear the vehicle rarely enters
Symptoms
- Engine speed higher than it used to be at a steady motorway speed
- Highway fuel economy declining while town driving feels unchanged
- Transmission appearing to hold fourth and never selecting top gear
- Code found during a scan for something unrelated, with no complaint at all
- Shop reporting no fault found after a short road test
- Slight slip felt only after a long period at constant speed
- Fluid temperature climbing on long journeys and normal around town
- Check engine light with the engine running exactly as normal
Diagnostic steps
- 1.Establish from service data how many forward ratios this transmission has and which element produces fifth, before any part is considered. Fifth is not a consistent physical thing across designs, and a generic answer to this code does not exist.
- 2.Check fluid level and condition on the manufacturer's procedure at the specified temperature. A level low enough to aerate only at sustained high speed produces exactly this pattern and is the cheapest outcome available.
- 3.Read every stored code. Ratio codes on other gears alongside this one move the problem to something shared and deeper in the transmission, and change both the diagnosis and the estimate.
- 4.Plan the road test properly, because this is the step that is usually skipped: a sustained run at motorway speed, light throttle, fluid fully warm. A lap of the industrial estate exercises first through fourth and never enters the gear the code is about.
- 5.Record the shaft speeds rather than reading them at the wheel. A passenger watches the scan tool, or the session is logged and reviewed when stopped — not studied at motorway speed by the driver.
- 6.Watch fluid temperature during that run and abort if it climbs beyond normal. A slipping element is putting heat into fluid that circulates through every other element, so extending the test to get a cleaner trace can cost more than the trace is worth.
- 7.Compare input and output shaft speed against the published fifth-gear ratio once the transmission has settled in top. Confirm the transmission actually reached fifth rather than holding fourth, since the symptom and the fault look similar in the data.
- 8.Check for shift solenoid codes and command the fifth-gear solenoid if the tool supports it, to separate a hydraulic or electrical routing fault from a worn element.
- 9.Look at the fluid for friction material before authorising internal work. A fault confined to top gear ought to leave clean fluid, and glitter in it says the problem is not confined at all.
- 10.Verify any repair with the same sustained high-speed run, warm, rather than a short drive — the only test that enters the gear this code concerns.
Repair cost
$150 – $3,400
Budget for the diagnosis honestly, because this one costs more than usual to confirm: a proper road test means sustained motorway running with a scan tool connected, not a lap of the industrial estate, and that is an hour of a technician's time rather than fifteen minutes. Expect $120 to $250 for diagnosis and treat a cheap quote here with suspicion, because a cheap diagnosis on this code is usually a short one. A fluid and filter service is $150 to $400. A solenoid is $200 to $600 fitted. An overdrive element or seal repair inside the unit is $1,500 to $3,400. The encouraging part is that a fault confined to top gear points at a smaller and shallower part of the transmission than a fault in the lower gears, so this is the version of this code with the best odds of landing at the lower end.
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DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.