OBD Code Index
Contributions welcome — this is a wiki. Anyone can edit this post. Add codes you’ve actually diagnosed, with the real fix that worked on your model/year. Keep “Common cause” honest (most likely first) and put model-specific quirks in “Notes.” Don’t paste copyrighted manuals — describe the procedure or link a legitimate source.
A running index of OBD-II diagnostic trouble codes that come up on Isuzu vehicles, with the usual suspects and what to check. This is a seed skeleton with a handful of representative generic (P0xxx) codes as examples — expand it.
How to use this: pull the code with a scanner, find it below, and start with the most common cause. A code points at a circuit or system, not always the part — don’t shotgun parts. When you fix one, come back and confirm what actually solved it. Tag your diagnostic threads with obd-codes plus the relevant system tag (e.g. fuel-system, cooling, electrical).
Codes below are generic OBD-II definitions shown as examples. Manufacturer-specific (Pxxxx in the P1/P30+ ranges) codes vary by model and year — add them in their own rows with the model noted.
Manual-swap note: On a truck that’s had an automatic-to-manual conversion, transmission codes like P0753 (shift solenoid A electrical) and P1860 (TCC PWM solenoid circuit) are expected — there’s no automatic left for the ECU to talk to. Treat them as noise, not a real fault. Tag those threads
manual-swap.
| Code | Meaning | Common cause | Notes |
|---|---|---|---|
| P0101 | Mass Air Flow (MAF) circuit range/performance | Dirty or failing MAF sensor; intake air leak after the MAF; restricted air filter | Clean the MAF before replacing. Check for cracked intake boots and loose clamps. |
| P0128 | Coolant temperature below thermostat regulating temperature | Stuck-open thermostat; faulty coolant temp sensor; engine not reaching operating temp | Confirm the engine actually warms up — a stuck-open thermostat is the usual culprit. See also cooling. |
| P0171 | System too lean (Bank 1) | Vacuum/intake leak; weak fuel pump or clogged filter; dirty MAF; leaking injector | Smoke-test for intake leaks first. On gas engines check fuel trims. |
| P0300 | Random/multiple cylinder misfire detected | Ignition (plugs/coils/wires), fuel delivery, vacuum leak, or low compression | Pair with cylinder-specific P030x codes to localize. Check for a stored cause before chasing the misfire blindly. |
| P0401 | Exhaust Gas Recirculation (EGR) flow insufficient | Clogged EGR passages/valve with carbon; stuck EGR valve; vacuum/electrical fault to the valve | Common on higher-mileage trucks. Clean before replacing. Do not tamper with emissions equipment where that’s illegal. |
| P0420 | Catalyst system efficiency below threshold (Bank 1) | Aged catalytic converter; exhaust leak; faulty downstream O2 sensor | Rule out exhaust leaks and a lazy rear O2 sensor before condemning the cat. |
| P0500 | Vehicle Speed Sensor (VSS) malfunction | Failed VSS; damaged wiring/connector; bad sensor ring/tone wheel | Affects speedo, shift behavior, and sometimes idle. Inspect the connector at the transfer case/transmission. |
| P0700 | Transmission Control System (MIL request) | A stored transmission code is present — P0700 is a flag, not the fault | Read the transmission-specific codes that accompany it. See also transmission. |
Adding a code
Copy a row, fill it in, and keep the table sorted by code number. If a code behaves differently on a specific model or year, say so explicitly in Notes — “on a [model/year], this usually means…” is exactly the kind of detail that saves someone a wasted afternoon.