Fault Codes

FOME reports problems as OBD-II style fault codes (DTCs). Most of them are standard P0xxx/P2xxx codes with their usual meanings, so a code you see here means roughly what it would mean on a factory ECU.

Reading a code

There are three places a fault shows up, and they don't all show the same thing.

In TunerStudio

The Last error and Error#1–Error#8 gauges show the eight most recent faults. They are shown as a plain decimal number, not as a P code. To convert, read the decimal number as hexadecimal — those digits are the P-code:

TunerStudio shows	Read as hex	Fault code
263	0x107	P0107
279	0x117	P0117
822	0x336	P0336
8501	0x2135	P2135

The tables below list both forms, so you can just look up the number you see.

The FOME console also prints a plain-English line when the fault happens, for example WARNING: Sensor fault: CLT input too low. That's usually faster to read than the code.

On the check engine light

If your board has a MIL output configured, it blinks stored codes out as hexadecimal digits, with a 1 second gap between digits and 5 seconds between codes. Each digit is blinked n+1 times, so 0 is one blink and 7 is eight blinks. P0107 blinks as 2, 1, 8.

Over CAN

FOME answers OBD-II service 0x03 (read stored DTCs) on the CAN bus, so a generic scan tool will read the codes normally. Pending and permanent DTCs (services 0x07 and 0x0A) are not supported.

Clearing codes

Stored codes live in RAM only, so power cycling the ECU clears them. Nothing is written to flash, and codes do not survive a reboot.

While the ECU is running, most sensor faults latch: once set, the code stays until reboot even if the sensor starts reading correctly again.

Choosing what a code does

Several codes have a configurable severity, set in TunerStudio next to the relevant sensor's settings (look for a "DTC Pxxxx severity" field):

• Warning only — the fault is logged, the code is stored, and the MIL is lit.
• Ignore — the fault is still logged as a warning, but no code is stored and the MIL stays off.

Use Ignore for codes that are noise on your setup — for example P0176 on a car with no flex sensor wiring, or the cam sensor codes on an engine where the cam signal is intentionally marginal.

Codes without a severity setting are always reported.

Sensor circuit codes

These come from the sensor checker, which runs once the ECU has been powered for a second and the battery voltage has been stable for 5 seconds. "Low"/"High" mean the raw input is outside the range that could possibly be real — almost always wiring, not calibration. "Timeout" means no reading has arrived at all.

Code	Dec	Meaning	What to check
P0101	257	MAF signal timeout	MAF unplugged, wrong pin assigned, no signal on the wire
P0102	258	MAF input below mafMinVoltage	Short to ground, open signal wire, or mafMinVoltage set too high for your sensor
P0103	259	MAF input above mafMaxVoltage	Short to 5V, open ground on the MAF, or mafMaxVoltage set too low
P0106	262	MAP signal timeout	MAP sensor unplugged or wrong input pin assigned
P0107	263	MAP below the configured minimum	Short to ground, broken signal wire, or mapErrorDetectionTooLow set too high for your sensor
P0108	264	MAP above the configured maximum	Short to 5V, missing sensor ground, or mapErrorDetectionTooHigh set too low for a boosted engine
P0110	272	IAT signal timeout	IAT input not configured or not sampling
P0112	274	IAT input below 0.05V	Sensor shorted to ground, or a short in the harness
P0113	275	IAT input above 4.9V	Open circuit — unplugged sensor, broken wire, or missing bias resistor
P0115	277	CLT signal timeout	CLT input not configured or not sampling
P0117	279	CLT input below 0.05V	Sensor or harness shorted to ground
P0118	280	CLT input above 4.9V	Open circuit — unplugged sensor or broken wire
P0120	288	TPS1 primary timeout	TPS input not configured or not sampling
P0122	290	TPS1 primary below tpsErrorDetectionTooLow	Open or shorted signal wire, or closed-throttle calibration is wrong
P0123	291	TPS1 primary above tpsErrorDetectionTooHigh	Short to 5V, or wide-open calibration is wrong
P0176	374	Flex sensor signal lost	Sensor unplugged, broken wire, or missing pull-up resistor on the signal line
P0178	376	Flex frequency too low (<45 Hz)	Marginal signal, noise, or a failing sensor
P0179	377	Flex frequency too high (>155 Hz)	Failing sensor, or methanol contamination in the fuel
P0196	406	Oil temperature signal timeout	Oil temp input not configured or not sampling
P0197	407	Oil temp input below 0.05V	Sensor or harness shorted to ground
P0198	408	Oil temp input above 4.9V	Open circuit — unplugged sensor or broken wire
P0220	544	TPS1 secondary timeout	Second TPS channel not configured or not sampling
P0222	546	TPS1 secondary too low	Open or shorted wire on the second TPS channel
P0223	547	TPS1 secondary too high	Short to 5V on the second TPS channel
P0225	549	TPS2 primary timeout	See P0120, for the second throttle body
P0227	551	TPS2 primary too low	See P0122
P0228	552	TPS2 primary too high	See P0123
P0521	1313	Oil pressure signal timeout	Oil pressure input not configured or not sampling
P0522	1314	Oil pressure below sensor range	Short to ground or broken signal wire
P0523	1315	Oil pressure above sensor range	Short to 5V, or the sensor's configured pressure range is too small
P2120	8480	TPS2 secondary timeout	See P0220, for the second throttle body
P2122	8482	TPS2 secondary too low	See P0222
P2123	8483	TPS2 secondary too high	See P0223
P2125	8485	Pedal primary timeout	Pedal input not configured or not sampling
P2127	8487	Pedal primary too low	Open or shorted pedal signal wire, or bad closed-pedal calibration
P2128	8488	Pedal primary too high	Short to 5V, or bad full-travel calibration
P2130	8496	Pedal secondary timeout	Second pedal channel not configured or not sampling
P2132	8498	Pedal secondary too low	Open or shorted wire on the second pedal channel
P2133	8499	Pedal secondary too high	Short to 5V on the second pedal channel
P2226	8742	Implausible barometric pressure at startup	MAP reading was not close to atmospheric when the ECU booted — check the MAP sensor calibration and that the engine was actually stopped

Redundancy correlation codes

Redundant sensor pairs (TPS and pedal) are cross-checked against each other. If the two channels disagree by more than 5% (10% on Hellen 121 Nissan), the combined sensor is invalidated:

Code	Dec	Meaning
P2135	8501	TPS1 primary and secondary disagree
P2136	8502	TPS2 primary and secondary disagree
P2137	8503	Pedal primary and secondary disagree

A correlation fault almost always means one of the two channels has drifted, is noisy, or was calibrated against the wrong end of its travel. Log both raw channels and compare them across the whole range of travel — they should track each other everywhere, not just at idle.

warning

On an electronic throttle car, a correlation fault will cut the throttle. Fix it before driving.

Trigger and cam codes

Code	Dec	Meaning	What to check
P0336	822	50+ crank trigger decode errors in one run	Noise on the crank signal, wrong trigger wheel selected, bad sensor gap, or a damaged reluctor
P0340	832	Bank 1 intake cam: no signal	Cam sensor unplugged, wrong input pin, or no signal reaching the ECU while the crank signal is fine
P0341	833	Bank 1 intake cam: 50+ decode errors	Noisy or intermittent cam signal, or the wrong VVT mode selected
P0345	837	Bank 2 intake cam: no signal	As P0340
P0346	838	Bank 2 intake cam: 50+ decode errors	As P0341
P0365	869	Bank 1 exhaust cam: no signal	As P0340
P0366	870	Bank 1 exhaust cam: 50+ decode errors	As P0341
P0385	901	Bank 2 exhaust cam: no signal	As P0340
P0386	902	Bank 2 exhaust cam: 50+ decode errors	As P0341

Cam codes are only checked once the crank trigger has synced 20 times, and only for cam inputs that actually have a pin assigned. Crank checking is skipped below the cranking RPM threshold so that a stalling engine doesn't set a code on the way down.

Knock sensor codes

Code	Dec	Meaning
P0327	807	Knock sensor 1 signal too low
P0332	818	Knock sensor 2 signal too low

Set when a knock sensor that was previously working reads below knockNoiseThreshold for longer than knockNoiseTimeout while the engine is running. A healthy sensor reads roughly -50 to -20 dBv; a disconnected one sits near the noise floor below -80 dBv. Check the sensor connector, the shield ground, and the sensor's mounting torque. Setting knockNoiseTimeout to 0 disables the check.

Injector and ignition circuit codes

Code	Dec	Meaning
P0201–P0212	513–530	Injector circuit 1–12 fault
P0351–P0362	849–866	Ignition circuit 1–12 fault

These require a board with smart driver chips capable of reporting output diagnostics — boards without them never set these codes. The TunerStudio console message includes the specific fault the driver reported (open load, short to ground, short to battery, over temperature). Check the injector or coil connector and the wiring to it first.

Power supply and system codes

Code	Dec	Meaning	What to check
P0612	1554	Main relay fault	The main relay voltage sense input reads more than 3V below battery voltage, 0.5s after the relay was commanded on. Check the relay, its fuse, and the wiring to the ECU's main relay feed
P0642	1602	5V sensor supply below 4.75V	A sensor is overloading or shorting the 5V rail. Unplug sensors one at a time to find it. Note that sensor checking is suspended while this is set
P0643	1603	5V sensor supply above 5.25V	ECU internal regulator problem, or something back-feeding the 5V rail
P0652	1618	Second 5V sensor supply low	As P0642, for boards with a second sensor supply (Proteus)
P2900	10496	Wideband controller 1 fault	The controller is reporting a fault of its own. The console message names it — usually sensor heater, sensor open, or overheating
P2901	10497	Wideband controller 2 fault	As P2900
P2902	10498	Wideband controller firmware too old	Update the wideband controller's firmware to match this FOME build

P2900–P2902 are FOME-specific codes, not standard OBD codes — a generic scan tool will not have a description for them.

Configuration errors

These are fatal — the ECU refuses to run the engine and TunerStudio shows a critical error banner with a message explaining the problem. They mean the tune is wrong, not that hardware failed. Fix the setting named in the message and reboot.

Code	Dec	Meaning
P0090	144	Injector compensation is set to use a fuel pressure sensor, but no sensor is configured
P0111	273	Thermistor calibration points are not in ascending temperature order
P0121	289	Throttle/pedal configuration problem — open and closed calibration voltages too close together, a redundant pair that isn't actually redundant, both channels of a "redundant" pair wired to one sensor, or a failed ETB autotune
P0606	1542	General ECU fault. Used for internal assertion failures and for prompting a power cycle after applying a preset. The console message says what happened
P0638	1592	ETB startup position was more than 5% away from the configured neutral position. Check for a stuck throttle plate, a wrong etbNeutralPosition, or bad TPS calibration
P2158	8536	An invalid CAN DBC was selected for CAN vehicle speed input

Internal codes (6000 and above)

Codes numbered 6000 and up are FOME internal diagnostics, not OBD codes. They aren't sent over CAN and they're rarely actionable — they indicate either a firmware bug or a configuration so far out of range that the firmware couldn't cope.

If you see one, the TunerStudio console message next to it is the useful part. Report the code together with that message and your tune on the Discord #firmware channel.

The full list is in firmware/controllers/algo/obd_error_codes.h.