sequenceDiagram
autonumber
Note over MemsFCR, ECU: Initialisation
MemsFCR ->>+ ECU: Connect
ECU ->>- MemsFCR: Connected
MemsFCR ->>+ ECU: 0xCA
Note right of ECU: Initialise Command A 
ECU ->>- MemsFCR: 0xCA
MemsFCR ->>+ ECU: 0x75
Note right of ECU: Initialise Command B
ECU ->>- MemsFCR: 0x75 
MemsFCR ->>+ ECU: 0xF4
Note right of ECU: Heartbeat
ECU ->>- MemsFCR: 0xF4 
MemsFCR ->>+ ECU: 0xD0
Note right of ECU: ECU ID
ECU ->>- MemsFCR: 0x0D 0x99 0x99 0x99 0x99 
Note over MemsFCR, ECU: Request Dataframe Loop
loop Every second
activate MemsFCR
MemsFCR ->>+ ECU: 0x7D
Note right of ECU: Dataframe 0x7D
ECU ->>- MemsFCR: 0x7D XX XX XX.. XX
MemsFCR ->>+ ECU: 0x80
Note right of ECU: Dataframe 0x80
ECU ->>- MemsFCR: 0x80 XX XX XX.. XX
deactivate MemsFCR
end

graph LR
FaultCodesDTC0("80x0d-0e_fault_codes (0x0d byte)") --> |& b00000001|CTSFault(["CTS_fault = true"])
FaultCodesDTC0 --> |& b00000010|ATSFault(["ATS_fault = true"])
FaultCodesDTC1("80x0d-0e_fault_codes (0x0e byte)") --> |& b00000010|FuelPumpFault(["fuel_pump_circuit_fault = true"])
FaultCodesDTC1 --> |& b01000000|TPSFault(["TPS_circuit_fault = true"])

If we have revs, the engine must be running :)
The engine start time is recorded to determine when the operating temperature is expected to be reached and when the O2 system should activate.

flowchart LR
Engine("80x01-02_engine-rpm (RPM) > 0") --> EngineRunning(["engine_running = true"])
EngineRunning --> EngineStartTime(["record engine_start_time"])

Used in the diagnostics to determine if the engine has reached the operating temperature.

flowchart LR
Temp{{"80x03_coolant_temp (CTS) > 80°C"}} -- "false" ---> EngineWarming(["engine_warming = true"])
Temp -- "true" ---> EngineWarm(["engine_at_operating_temp = true"])

RPM can't be used as a reliable indicator of idle so the throttle is used to determine whether the engine is at idle.

flowchart LR
Running(engine_running) --> Metric
Metric("7dx02_throttle_angle * 6 / 10 <= 14&deg") --> Result([engine_idle = true])

If the RPM is above any cold start value OR the throttle is depressed (14° is pretty conservative) then the throttle is active.

flowchart LR
Engine("80x01-02_engine-rpm (RPM)> 1300") --> ThrottleActive(["throttle_active = true"])
Throttle("7dx02_throttle_angle * 6 / 10 > 14°") --> ThrottleActive

The ECU controls the air : fuel mix based on the readings from the primary sensors, lambda, MAP and temperature.
If the ECU determines these systems are working correctly it will enter closed loop mode. The car is unlikely to pass the emissions tests if it cannot enter closed loop mode.

flowchart LR
Temp("7dx0A_closed_loop > 0") --> ClosedLoop(["closed_loop = true"])

The battery voltage is important for the sensors to provide correct values. A low battery can be the cause of a number of phantom faults.ß

flowchart LR
Metric("80x08_battery_voltage < 13V") --> Result(["battery_low = true"])

The time for the ignition coil to charge up to its specified current, as measured by the MEMS ECU. With a battery voltage of about 14V, this value should be about 2-3mS.
A high value for coil charge time may indicate a problem with the ignition coil primary circuit. A failing CAS sensor can also cause the coil time to increase.

flowchart LR
Running("engine_running") --> BatteryCheck
BatteryCheck("battery_low = false") --> Metric
Metric("80x17-18_coil_time * 0.0002 > 4ms") --> Result(["coil_fault = true"])

The MAP sensor should be under 45kPA (ideally 35kPA) when the engine is at idle. A high value indicates a vacuum fault.

flowchart LR
Running("engine_idle") --> Metric
Metric("80x07_map_kpa > 45") --> Result(["map_fault = true"])

This Idle Base Position is the number of steps from 0 which the ECU will use as guide for starting idle speed control during engine warm up.
The value will start at quite a high value (>100 steps) on a very cold engine and fall to < 50 steps on a fully warm engine. A high value on a fully warm engine or a low value on a cold engine will cause poor idle speed control.
Idle position is calculated by the ECU using the engine coolant temperature sensor.

flowchart LR
Running("engine_idle = true") --> EngineAtTemp{{"engine_at_operating_temp"}}
EngineAtTemp -- "true" ---> MetricHot
EngineAtTemp -- "false" ---> MetricCold
MetricHot("7dx0F_idle_base_pos > 55") --> Result(["idle_fault = true"])
MetricCold("7dx0F_idle_base_pos < 45") --> Result(["idle_fault = true"])

The Hot Idle is the number of IACV steps from fully closed (0) which the ECU has learned as the correct position to maintain the target idle speed with a fully warmed up engine.
If this value is outside the range 10 - 50 steps, then this is an indication of a possible fault condition or poor adjustment.

flowchart LR
Running("engine_idle") --> PreCheck
PreCheck("engine_at_operating_temp = true") --> EngineAtTemp
EngineAtTemp ---> MetricLow
EngineAtTemp ---> MetricHigh
MetricLow("80x10_idle_hot < 10") ---> Result(["idle_hot_fault = true"])
MetricHigh("80x10_idle_hot > 55") ---> Result(["idle_hot_fault = true"])

The stepper motor adjusts the idle air control valve (IACV) and is used to control engine idle speed and air flow from cold start up
A high number of steps indicates that the ECU is attempting to close the stepper or reduce the airflow a low number would indicate the inability to increase airflow

The position of the IACV stepper motor as calculated by the ECU. The ECU has no method of actually measuring this position but instead works it out by remembering how may steps it has moved the stepper since the last time the ignition was switched off. If a stepper motor fault exists, this number will be incorrect. This value will normally be changing during idle condition as the ECU makes minor changes to the idle speed. A value of 0 during idle conditions indicates a fault condition or poor adjustment, as does a very high value.

flowchart LR 
Running("engine_idle") --> PreCheck
PreCheck("7dx13_idle_speed_offset > 50") --> Metric
Metric("80x12_iac_position > 0") --> Result(["iac_fault = true"])

The bane of all Mini Spi owners, the vacuum pipe system to read the manifold absolute pressure is fragile and prone to split or disconnected pipes.
The MAP values are essential for the ECU to determine the load on the engine and have a significant impact on performance and even basic idling.
When the engine is at idle, the MAP is expected to be less than 45kPa, in fact it should be around 35kPA. Higher than this will be due to a vacuum fault.

flowchart LR
Running("engine_idle") --> Metric
Metric("80x07_map_kpa > 45") --> Result(["vacuum_fault = true"])

On systems using a throttle body where the idle air is controlled by a stepper motor which directly acts on the throttle disk (normally metal inlet manifold), the count indicates the number of times the ECU has had to re-learn the relationship between the stepper position and the throttle position. If this count is high or increments each time the ignition is turned off, then there may be a problem with the stepper motor, throttle cable adjustment or the throttle pot. On systems using a plastic throttle body/manifold, the count is a warning that the MEMS ECU has never seen the throttle fully closed. The count is increased for each journey with no closed throttle, indicating a throttle adjustment problem.
This "fault" is more of an indication that the jack count is higher than expected and is worth monitoring this value.

flowchart LR
Running("engine_idle") --> Metric
Metric("7dx1F_jack_count > 50") --> Result(["iac_jack_fault = true"])

The crankshaft sensor is used to determine the position of the engine so the ECU can manage the timing of the injection of fuel and ignition.
A failing CAS will show as 0 entries or high spikes in the graph trace. When the ECU fails to get a CAS reading, it will suspend firing the ignitions (this will show as a high coil time)

flowchart LR
Metric("80x19_crankshaft_position_sensor is 0") --> Result(["crankshaft_sensor_fault = true"])

When the engine is running the lambda sensor voltage is expected to oscillate low to high rapidly.
If the readings are above 900mV or below 10mV this indicates a failing lambda sensor.

flowchart LR
Running("engine_running") --> MetricLow
Running ---> MetricHigh
MetricLow("7dx06_lambda_voltage < 10") ---> Result(["lambda_range_fault = true"])
MetricHigh("7dx06_lambda_voltage > 900") ---> Result(["lambda_range_fault = true"])

When the engine is started the lambda sensor goes through a warm-up cycle.
The lambda has a build in heater and the ECU activates this via a relay.
The lambda should start oscillating from low to high volts after around 90s.
A failure in this activity will cause the ECU to change the lambda status to 0 and run in open loop mode. This is a fault condition.

flowchart LR
Running("engine_running") --> PreCheck
PreCheck("time since engine_start_time > 90s") --> IsOscillating
subgraph Is Lambda Sensor oscillating?
    IsOscillating("standard deviation of 7dx06_lambda_voltage < 100") --> Result(["lambda_oscillation_fault = true"])
end
Result --> Metric
Metric{{"lambda_oscillation_fault is false"}} --> LambdaResult(["lambda_fault = true"])

flowchart LR
Metric("7dx09_lambda_sensor_status = 0") --> Result(["o2_system_fault = true"])

The lambda sensor should oscillate low to high voltage at a high frequency.
A sample is used for calculating the standard deviation, which is used to determine whether the lambda is working as expected.

flowchart LR
Running("engine_running") --> Metric
Metric("standard deviation of 7dx06_lambda_voltage < 100") --> Result(["lambda_oscillation_fault = true"])

The coolant temperature is expected to rise at a rate of around 11s per degree.
If the coolant temperature hasn't reached operating temperature (80°C) by that time, this indicates the thermostat could be faulty.

flowchart LR
Running("engine_running") --> Step1
subgraph Determine if the coolant temperature has reached operating temp as expected
Step1("degrees_to_warm = 80°C - 80x03_coolant_temp") --> Step2
Step2("expected_time_to_warm = 11s * degrees_to_warm") --> Step3
Step3("current_time > expected_time_to_warm") --> Step4
end
Step4("80x03_coolant_temp < 80&deg;C") --> Result(["thermostat_fault = true"])

Idle speed deviation indicates how far away the IAC is from the idle target
Idle base position indicates the target for IAC position A mean value of more than 100 indicates that the ECU is not in control of the idle speed and indicates a possible fault condition.

flowchart LR
Running("engine_running") --> Metric
Metric("mean of 7dx0F_idle_base_pos > 100") --> Result(["idle_speed_fault = true"])