THE CODE DIRECTORY

Diagnostic code references — Page 23.

Browse canonical reference entries. Each definition keeps its own source and vehicle-applicability limits.

Generic OBD-II

P0601

These are code references, not a list of confirmed faults on every vehicle. Read the source and applicability notes, then match the exact vehicle, year, engine and scan report.

checksum and flash-memory integrity failures

programming status depends on which module reports it

nonvolatile-memory checks occur at both startup and shutdown

RAM integrity checks cover several different memory paths

A TCM flash-memory read error is different from a checksum complaint

processor-integrity faults require the reporting module

built-in self-tests and memory error counters

Control Module VSS Output A

Vehicle-speed output channel feedback disagrees with its command

Processor-performance codes need the reporting module identified

internal analog-conversion checks are not external sensor thresholds

redundant calculations reveal processor-performance problems

Pedal plausibility includes signal scaling and learned values

Throttle-angle monitoring inside the DME

Internal Control Module Coolant Temperature Performance

A TCM recovery reset differs from the generic vehicle-options label

This diesel injector-module fault monitors an internal voltage quantity

Fuel Injector Control Module Relay Control

TCM processor diagnosis can identify an operating-system startup fault

ECM/TCM Incompatible

starter relay open-circuit checking occurs with the driver off

starter relay low voltage is judged in the off state

starter relay high voltage during an on command

Alternative Fuel Control Module KAM Error

Alternative Fuel Control Module RAM/ROM Error

Torque supervision can fail without a check-engine light

One torque-calculation code can describe different supervised events

internal engine-speed calculation versus measured speed

Internal airmass supervision is different from a MAF sensor circuit code

Internal Control Module Brake Signal Performance

Throttle-controller supervision is a different layer from motor wiring

Alternator output monitoring and occurrence history

generator L-terminal integrity is a circuit check

generator field-feedback duty cycle needs operating context

Generator Lamp Control Circuit

Fuel Cap Lamp Control Circuit

A low generator F-terminal duty cycle is checked with the engine running

The high F-terminal test belongs to a stationary key-on starting state

feed-fuel-pump relay driver detects an open load

fuel-pump relay control short-to-ground signature

fuel-pump relay output stays high while commanded off

Lift-pump feedback leaves its narrow duty-cycle window

fuel-injector driver integrity has several internal failure paths

Vehicle-speed supervision is not simply a missing speed-sensor signal

injector-driver boost voltage outside its operating window

Bank-two injector-driver performance concerns the high-voltage supply

EEPROM performance is module specific

invalid programmed VIN characters in the ECM

VIN Not Programmed or Incompatible - TCM

Missing wheel-circumference programming in a GM example

missing immobilizer programming is not the same as a wrong response

TCM substrate heat and excess supply voltage have separate trigger paths

Power Steering Control Circuit

Power Steering Control Circuit Low

Power Steering Control Circuit High

bank-1 throttle duty-cycle demand exceeds its limit

bank-2 throttle effort and supply-voltage compensation

Generator Voltage Sense Circuit A

Generator voltage-sense fault reported through the PCM

Generator voltage-sense low input inside the ISG

ISG voltage measurements disagree with an internal high signal

Auto Configuration Throttle Input Not Present Bank 1

Auto Configuration Engine Coolant Temperature Input Not Present

Intake-heater control response while heating is commanded off

reference A can fail through instability as well as level

Reference A low is a qualified supply-rail measurement

Reference A high must be distinguished from high battery supply

Driver Display Serial Communication Circuit

A/C clutch-relay command disagrees with circuit feedback

A/C clutch relay control stays electrically low

A/C clutch relay control stays electrically high

Immobilizer Lamp Control Circuit

Speed Control Lamp Control Circuit

Fuel-pump module diagnosis includes timing and command plausibility

PTO Control Module

Glow-plug controller performance can include supply problems

bank-one oxygen-sensor processing can fail internally

bank-2 oxygen-interface processor self-checks

invalid authentication table in ECU software

A failed warning-lamp circuit can store a code without illuminating the lamp