Hi everyone,
I’m trying to diagnose a very strange intermittent electrical/engine management fault on my 2020 Toyota GR Yaris Circuit Pack, and I’d really appreciate some input from people who know these cars well.
The problem started after an Eventuri intake was installed. When I went to collect the car, the mechanic told me that during the installation a fault had appeared and it was very difficult to clear, although he eventually managed to erase it. I then drove around 50 km and, after going over a bump, the fault appeared for the first time.
The very first DTC was related to the electronic throttle body.
Since then, the fault has been intermittent. Sometimes the car can go for a long time with no issue at all, and other times it can happen several times within a short distance.
When the fault happens, the car goes into reduced power / limp mode. The throttle response becomes extremely limited, the engine will barely rev, and several warning lights come on at the same time, including the engine warning light plus ABS / PCS / AWD-related warnings.
When the fault is active, the engine can sound slightly out of rhythm or “off beat”, although if I manage to raise the revs slightly it usually sounds a bit better.
Most of the time, the fault originally appeared at low rpm or when the engine was at idle, but more recently it has also happened while driving under load.
One recent example was during acceleration at roughly 2,000–3,000 rpm. The car suddenly lost power almost instantly. It did not feel like overboost protection and it was definitely not an rpm limiter. It felt more like somebody had switched the ignition off for a fraction of a second, or like the throttle had suddenly disappeared.
On other occasions it has happened when approaching a roundabout or lifting off the accelerator.
There is also another symptom that I think may be important. The idle itself can be completely stable and normal, but then suddenly, for just a fraction of a second, the engine behaves as if the ignition has been disconnected. The revs drop by roughly 300 rpm, it feels like the engine is about to stall, and then it immediately recovers and continues idling normally.
On one occasion this happened about three times while parked in the garage, after I had driven the car hard for around 30 minutes with absolutely no problem. After the third brief “micro-cut”, the usual fault finally appeared and the car went into limp mode.
I originally suspected the battery because the original battery was around six years old, but the battery has now been replaced with a new one and the problem remains.
Another important point is the ECU connector and wiring.
The main ECU connector is not in perfect condition. The locking mechanism / clip is damaged, and I have also found some damaged or exposed wiring in the area.
Several times, when the fault has appeared, I have disconnected the ECU connectors and reconnected them. Sometimes the car still starts with the fault present on the first attempt, but after disconnecting and reconnecting the ECU again it starts and runs perfectly.
For example, recently the car faulted immediately after starting. I disconnected and reconnected the ECU, but the fault remained. I did it a second time and the car then ran perfectly. I drove around 2 km and the fault came back. I repeated the ECU disconnect/reconnect procedure a couple of times until it worked again. I then drove another 5 km, the fault returned again, and after reconnecting the ECU it ran normally for another 7 km.
On another day, after reconnecting the ECU, the car ran perfectly for around 30 minutes of hard driving with no hesitation at all, and only started showing the micro-cut behaviour once I had stopped and was idling in the garage.
However, simply moving the ECU loom or touching the wires while the engine is running normally does not reproduce the fault.
Because the fault started immediately after the Eventuri installation, I also wondered whether something from the original intake wiring may have been left disconnected. Some of the original intake-related wiring/connectors were no longer used after the Eventuri installation.
As far as I understand, the intake itself does not use CAN directly, but I am wondering whether a sensor supply, ground, throttle-related circuit, MAF-related circuit, or wiring disturbed during the intake installation could be causing the issue.
At the moment my main suspicions are:
The reason I am particularly suspicious of the ECU connector/wiring is that physically disconnecting and reconnecting the ECU sometimes changes the condition of the fault, although I realise this may also simply be resetting the ECU and clearing the fail-safe state temporarily.
The fact that the very first DTC after the Eventuri installation was throttle-body related also makes me suspicious of the electronic throttle control circuit.
What I would really like to know is:
Has anyone seen a similar intermittent fault on a GR Yaris where the engine suddenly loses throttle / torque for a fraction of a second, drops into limp mode, and simultaneously throws multiple ABS / PCS / AWD warnings?
Also, has anyone had issues with ECU connector terminals, wiring close to the ECU, throttle-body wiring, CKP/CMP wiring, or damaged pins on these cars?
My next step is to capture every DTC immediately when the fault happens, without switching the ignition off or disconnecting the ECU, so I can separate the primary fault from the secondary communication faults.
Any advice on specific pins, circuits, common loom failure points, throttle-body wiring or ECU connector issues would be very welcome.
I’m trying to diagnose a very strange intermittent electrical/engine management fault on my 2020 Toyota GR Yaris Circuit Pack, and I’d really appreciate some input from people who know these cars well.
The problem started after an Eventuri intake was installed. When I went to collect the car, the mechanic told me that during the installation a fault had appeared and it was very difficult to clear, although he eventually managed to erase it. I then drove around 50 km and, after going over a bump, the fault appeared for the first time.
The very first DTC was related to the electronic throttle body.
Since then, the fault has been intermittent. Sometimes the car can go for a long time with no issue at all, and other times it can happen several times within a short distance.
When the fault happens, the car goes into reduced power / limp mode. The throttle response becomes extremely limited, the engine will barely rev, and several warning lights come on at the same time, including the engine warning light plus ABS / PCS / AWD-related warnings.
When the fault is active, the engine can sound slightly out of rhythm or “off beat”, although if I manage to raise the revs slightly it usually sounds a bit better.
Most of the time, the fault originally appeared at low rpm or when the engine was at idle, but more recently it has also happened while driving under load.
One recent example was during acceleration at roughly 2,000–3,000 rpm. The car suddenly lost power almost instantly. It did not feel like overboost protection and it was definitely not an rpm limiter. It felt more like somebody had switched the ignition off for a fraction of a second, or like the throttle had suddenly disappeared.
On other occasions it has happened when approaching a roundabout or lifting off the accelerator.
There is also another symptom that I think may be important. The idle itself can be completely stable and normal, but then suddenly, for just a fraction of a second, the engine behaves as if the ignition has been disconnected. The revs drop by roughly 300 rpm, it feels like the engine is about to stall, and then it immediately recovers and continues idling normally.
On one occasion this happened about three times while parked in the garage, after I had driven the car hard for around 30 minutes with absolutely no problem. After the third brief “micro-cut”, the usual fault finally appeared and the car went into limp mode.
I originally suspected the battery because the original battery was around six years old, but the battery has now been replaced with a new one and the problem remains.
Another important point is the ECU connector and wiring.
The main ECU connector is not in perfect condition. The locking mechanism / clip is damaged, and I have also found some damaged or exposed wiring in the area.
Several times, when the fault has appeared, I have disconnected the ECU connectors and reconnected them. Sometimes the car still starts with the fault present on the first attempt, but after disconnecting and reconnecting the ECU again it starts and runs perfectly.
For example, recently the car faulted immediately after starting. I disconnected and reconnected the ECU, but the fault remained. I did it a second time and the car then ran perfectly. I drove around 2 km and the fault came back. I repeated the ECU disconnect/reconnect procedure a couple of times until it worked again. I then drove another 5 km, the fault returned again, and after reconnecting the ECU it ran normally for another 7 km.
On another day, after reconnecting the ECU, the car ran perfectly for around 30 minutes of hard driving with no hesitation at all, and only started showing the micro-cut behaviour once I had stopped and was idling in the garage.
However, simply moving the ECU loom or touching the wires while the engine is running normally does not reproduce the fault.
Because the fault started immediately after the Eventuri installation, I also wondered whether something from the original intake wiring may have been left disconnected. Some of the original intake-related wiring/connectors were no longer used after the Eventuri installation.
As far as I understand, the intake itself does not use CAN directly, but I am wondering whether a sensor supply, ground, throttle-related circuit, MAF-related circuit, or wiring disturbed during the intake installation could be causing the issue.
At the moment my main suspicions are:
- ECU connector / poor terminal contact
- broken wire inside the loom close to the ECU
- intermittent ECU power supply or ground
- electronic throttle body circuit or wiring between the throttle body and ECU
- crankshaft position sensor (CKP) or camshaft position sensor (CMP) signal issue
- less likely, an internal ECU fault
The reason I am particularly suspicious of the ECU connector/wiring is that physically disconnecting and reconnecting the ECU sometimes changes the condition of the fault, although I realise this may also simply be resetting the ECU and clearing the fail-safe state temporarily.
The fact that the very first DTC after the Eventuri installation was throttle-body related also makes me suspicious of the electronic throttle control circuit.
What I would really like to know is:
Has anyone seen a similar intermittent fault on a GR Yaris where the engine suddenly loses throttle / torque for a fraction of a second, drops into limp mode, and simultaneously throws multiple ABS / PCS / AWD warnings?
Also, has anyone had issues with ECU connector terminals, wiring close to the ECU, throttle-body wiring, CKP/CMP wiring, or damaged pins on these cars?
My next step is to capture every DTC immediately when the fault happens, without switching the ignition off or disconnecting the ECU, so I can separate the primary fault from the secondary communication faults.
Any advice on specific pins, circuits, common loom failure points, throttle-body wiring or ECU connector issues would be very welcome.
