Two GT-Rs, the Same Intermittent Problem
It is not uncommon for us to see the same fault appear on multiple cars within a short period. In this case, a pair of early-model Nissan R35 GT-Rs arrived at the workshop within days of each other, both presenting with intermittent gear selection issues. One owner described occasional hesitation when pulling away from traffic lights. The other reported the drivetrain warning light flickering on under hard acceleration before disappearing again on the next drive cycle. In both cases, the cars were still driveable, and in both cases, the owners had been living with the issue for a while, hoping it would sort itself out.
It will not sort itself out. On the R35 GT-R, intermittent drivetrain faults that are ignored have a habit of escalating into catastrophic and extremely expensive transmission failures. Both owners made the right call bringing their cars in before the problem got worse.
Understanding the GR6 Dual-Clutch Transmission
To understand why these faults occur and why they require careful diagnosis, it helps to understand what the GR6 transmission actually is. The R35 GT-R uses a rear-mounted, transaxle-style dual-clutch gearbox. It is not a conventional automatic or a traditional manual. The GR6 has two clutch packs, one controlling the odd gears and one controlling the even gears, which allows it to pre-select the next gear before the current shift is complete. The result is seamless, lightning-fast gear changes that are a defining characteristic of the GT-R driving experience.
The system relies entirely on precise hydraulic control. A network of pressure sensors monitors line pressure, clutch pack pressure, and shift actuator pressure throughout the gearbox. Solenoids control the flow of transmission fluid to engage and disengage clutches, actuate gear selection forks, and manage the torque transfer between clutch packs during shifts. The Transmission Control Module (TCM) reads all of these inputs in real time and makes decisions measured in milliseconds. When every sensor is reading accurately and every solenoid is responding within specification, the system works beautifully. When a sensor drifts or a solenoid develops an intermittent fault, the consequences range from subtle shift hesitation to complete loss of gear engagement.
Why Static Fault Codes Are Not Enough
The challenge with diagnosing intermittent GR6 faults is that static fault codes often do not tell the full story. A pressure sensor that is drifting out of specification might only produce an out-of-range reading under specific conditions, such as when the transmission is at operating temperature and under load in a particular gear. A solenoid with an intermittent electrical fault might test perfectly when checked with a multimeter on the bench but fail to respond quickly enough under the rapid cycling that occurs during a fast upshift.
This is where the diagnostic approach matters. Rather than plugging in a scan tool, reading the stored codes, and replacing whatever part the code points to, we took a methodical approach. Both cars were instrumented with live TCM data logging and driven across multiple drive cycles under varied conditions: cold start, city traffic, highway cruise, and hard acceleration through the gears. The goal was to capture the fault as it occurred in real time, not rely on a snapshot stored in the TCM’s memory after the fact.
Isolating the Root Cause
The logged data from both cars told a clear story. On both GT-Rs, the gearbox pressure sensors were drifting out of their calibrated range under sustained thermal load. The readings would start within specification when the transmission was cold and gradually drift as the fluid reached operating temperature, eventually reaching a point where the TCM’s shift strategy could not compensate for the inaccurate pressure data. This manifested as the hesitant shifts and the occasional drivetrain warning.
On one of the two cars, we also identified a solenoid response time issue. The solenoid was physically operational, but its response time had degraded to the point where it could not cycle fast enough to meet the TCM’s demands during rapid gear changes. Under gentle driving, the slower response was masked. Under hard acceleration or fast downshifts, the delay was enough to cause a momentary loss of clutch pressure, which the TCM flagged as a fault.
This is a well-documented failure pattern on pre-2012 R35 GT-Rs. The early sensors and solenoids accumulate wear from the high cycle counts and thermal stress inherent to the GR6’s operation, and their performance degrades gradually over tens of thousands of kilometres. It is not a sudden failure; it is a slow drift that eventually crosses the threshold of what the TCM can tolerate.
The Fix and Verification
The affected pressure sensors and solenoids were replaced on both cars. With the new components installed, the transmission was re-adapted using the factory procedure. Re-adaptation is critical on the GR6 because the TCM learns clutch engagement points, shift pressure targets, and timing calibrations based on the specific hardware in the gearbox. If you replace sensors or solenoids without re-adapting, the TCM is still using learned values based on the old, degraded components, and the new parts will not perform to their potential.
After re-adaptation, both cars were road-tested under the same conditions that previously triggered the faults. Multiple drive cycles through cold start, warm-up, city driving, highway cruise, and hard acceleration confirmed that the faults had not returned. Shift quality on both cars was restored to the crisp, seamless engagement that the GR6 is capable of when everything is working within specification.
Catching It Early Saved Both Owners
The important takeaway from this job is what did not happen. A drifting pressure sensor that is ignored will eventually cause the TCM to apply incorrect clutch pressures during shifts. Incorrect clutch pressures lead to clutch slip, which generates heat, which accelerates clutch wear, which leads to burnt clutch packs and a full transmission rebuild that costs tens of thousands of dollars. A slow solenoid that is ignored can cause hard engagements that shock-load the gear train and damage synchroniser rings.
Both of these owners caught the issue at the sensor and solenoid stage. The repair bill for replacing these components and re-adapting the transmission is a fraction of what a full GR6 rebuild costs. If you own an early R35 and you have noticed any hesitation in shifts, any intermittent drivetrain warnings, or any behaviour that does not feel right, do not wait for it to get worse. The GR6 is a remarkable piece of engineering, but it requires proper diagnosis and maintenance to keep it performing as Nissan intended.