DOCUMENTED DIAGNOSTIC CONTEXT

Diagnostic code articles — Page 12.

Understand what the recorded fault means, which findings change the diagnosis, and what the cited documentation can confirm. Each article states the system or vehicle scope it covers.

Some sources leave details unresolved. Those articles include a visible source note; a code match alone does not establish applicability to your vehicle.

4,000 code articles

Generic OBD-II
P0638

bank-1 throttle duty-cycle demand exceeds its limit

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Generic OBD-II
P0639

bank-2 throttle effort and supply-voltage compensation

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Generic OBD-II
P063B

Generator voltage-sense fault reported through the PCM

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Generic OBD-II
P063C

Generator voltage-sense low input inside the ISG

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Generic OBD-II
P063D

ISG voltage measurements disagree with an internal high signal

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Generic OBD-II
P0640

Intake-heater control response while heating is commanded off

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Generic OBD-II
P0641

reference A can fail through instability as well as level

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Generic OBD-II
P0642

Reference A low is a qualified supply-rail measurement

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Generic OBD-II
P0643

Reference A high must be distinguished from high battery supply

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Generic OBD-II
P0645

A/C clutch-relay command disagrees with circuit feedback

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Generic OBD-II
P0646

A/C clutch relay control stays electrically low

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Generic OBD-II
P0647

A/C clutch relay control stays electrically high

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Generic OBD-II
P064A

Fuel-pump module diagnosis includes timing and command plausibility

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Generic OBD-II
P064C

Glow-plug controller performance can include supply problems

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Generic OBD-II
P064D

bank-one oxygen-sensor processing can fail internally

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Generic OBD-II
P064E

bank-2 oxygen-interface processor self-checks

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Generic OBD-II
P064F

invalid authentication table in ECU software

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Generic OBD-II
P0650

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

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Generic OBD-II
P0651

reference circuit 2 has a separate stability monitor

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Generic OBD-II
P0652

Reference B low identifies the second TCM reference rail

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Generic OBD-II
P0653

transmission sensor-reference supply 2 is high

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Generic OBD-II
P0657

an actuator-supply open-load result saved at shutdown

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Generic OBD-II
P0658

shared actuator supply is checked while switched on

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Generic OBD-II
P0659

An actuator supply high fault can be discovered during shutdown

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Generic OBD-II
P065A

Generator performance compares alternator and battery information

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Generic OBD-II
P065E

Intake-manifold feedback must agree with a stable command

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Generic OBD-II
P0660

An intake tuning valve output fault is an electrical check

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Generic OBD-II
P0661

The intake tuning valve reports an output-one ground-short status

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Generic OBD-II
P0662

Read the reported tuning-valve fault separately from its inconsistent heading

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Generic OBD-II
P0666

The transmission control module temperature-sensor circuit

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Generic OBD-II
P0667

TCM substrate temperature must agree with two other measurements

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Generic OBD-II
P0668

A very low TCM substrate reading is treated as a circuit fault

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Generic OBD-II
P0669

An implausibly high substrate reading requires a valid operating context

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Generic OBD-II
P066A

cylinder 1 glow circuit low and the inrush check

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Generic OBD-II
P066B

cylinder 1 glow output short toward power

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Generic OBD-II
P066C

cylinder 2 glow control ground-short monitoring

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Generic OBD-II
P066D

load-dependent high-voltage fault on glow circuit 2

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Generic OBD-II
P066E

cylinder 3 glow circuit low versus excessive initial current

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Generic OBD-II
P066F

cylinder 3 glow circuit high has two load-dependent cases

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Generic OBD-II
P0670

Ford 7.3L glow-plug control-line fault

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Generic OBD-II
P0671

cylinder 1 glow-plug open-load diagnosis

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Generic OBD-II
P0672

open circuit detected on cylinder 2 glow output

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Generic OBD-II
P0673

cylinder 3 glow circuit appears electrically unloaded

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Generic OBD-II
P0674

cylinder 4 glow output open-load monitoring conditions

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Generic OBD-II
P0675

cylinder 5 glow open-load monitor with a source-label conflict

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Generic OBD-II
P0676

cylinder 6 glow circuit open-load evidence

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Generic OBD-II
P0677

Cylinder7 glow-plug open monitoring requires an active heating command

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Generic OBD-II
P0678

Cylinder8 open-load evidence depends on glow heating mode

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Generic OBD-II
P0679

Touareg V10 cylinder 9 glow-plug circuit

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Generic OBD-II
P067A

cylinder 4 glow ground-short and inrush-current assessment

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Generic OBD-II
P067B

cylinder 4 glow-plug high-circuit detection

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Generic OBD-II
P067C

cylinder 5 glow-plug low circuit and inrush faults

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Generic OBD-II
P067D

understanding the cylinder 5 glow-plug high fault

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Generic OBD-II
P067E

cylinder 6 low-circuit detection has a startup branch

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Generic OBD-II
P067F

cylinder 6 glow-plug output high-circuit fault

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Generic OBD-II
P0683

Ford glow-plug module communication check

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Generic OBD-II
P0684

Volkswagen CJAA glow-controller communication fault

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Generic OBD-II
P0685

powertrain relay open-circuit detection uses the off state

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Generic OBD-II
P0686

low power-relay control voltage can overlap an open fault

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Generic OBD-II
P0687

power-relay control high with an unresolved state conflict

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Generic OBD-II
P0688

J271 load-circuit failure can explain fan or no-start complaints

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Generic OBD-II
P0689

relay feedback remains low when the relay is on

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Generic OBD-II
P068A

A relay that de-energizes too early is a timing classification

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Generic OBD-II
P068C

Cylinder7 glow-control low is a short-to-ground classification

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Generic OBD-II
P068D

Zero current alone cannot distinguish every glow-plug fault

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Generic OBD-II
P068E

Cylinder8 glow-control low uses a different category from open load

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Generic OBD-II
P068F

Cylinder8 high-circuit evidence needs the driver’s classification

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Generic OBD-II
P0690

relay feedback stays high after an off command

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Generic OBD-II
P0691

cooling-fan relay control is unexpectedly low while off

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Generic OBD-II
P0692

cooling-fan control stays high during an on command

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Generic OBD-II
P0693

Fan2 circuit low can include an open relay circuit in this Ford monitor

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Generic OBD-II
P0694

Fan2 high-control monitoring reports a short-to-power category

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Generic OBD-II
P0695

Fan relay 3 low-side diagnostic can also indicate an open circuit

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Generic OBD-II
P0696

Fan relay 3 driver reports a high-circuit condition

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Generic OBD-II
P0697

reference circuit 3 faults include rapid variation

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Generic OBD-II
P0698

Reference voltage C is low, but the code does not name the attached sensor

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Generic OBD-II
P0699

A high five-volt reference needs a supply-level diagnosis

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Generic OBD-II
P069E

The ECM is forwarding a fuel-controller fault request

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Generic OBD-II
P06A0

Ford variable-displacement A/C diagnosis before compressor replacement

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Generic OBD-II
P06A1

Variable compressor valve control circuit low

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Generic OBD-II
P06A2

Variable compressor valve control circuit high

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Generic OBD-II
P06A3

reference D means the fourth monitored ECM reference

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Generic OBD-II
P06A4

transmission speed-sensor supply 1 undervoltage

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Generic OBD-II
P06A5

Reference D high can be a 10.5-volt speed-sensor supply check

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Generic OBD-II
P06A6

Sensor reference A can invalidate several otherwise unrelated monitors

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Generic OBD-II
P06A7

Sensor reference B is a separate monitored supply group

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Generic OBD-II
P06A8

Sensor reference C needs its own circuit identification

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Generic OBD-II
P06AC

Powerup temperature plausibility depends on two independent differences

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Generic OBD-II
P06AD

A low powerup-temperature signal has load and speed prerequisites

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Generic OBD-II
P06AE

An extreme powerup-temperature reading is a circuit diagnosis

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Generic OBD-II
P06AF

engine shutdown code can reflect controller pattern monitoring

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Generic OBD-II
P06B1

speed-sensor supply switch current or temperature fault

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Generic OBD-II
P06B2

Motor A sensor power is a 15-volt rail in this implementation

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Generic OBD-II
P06B4

Sensor supply B low may originate from a protective switch report

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Generic OBD-II
P06B5

Motor B has a separate high sensor-supply diagnosis

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Generic OBD-II
P06B6

the knock-monitor test circuit has its own diagnostic

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Generic OBD-II
P06B7

The knock-processor test is not a measurement of engine knock

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Generic OBD-II
P06B8

NVRAM monitoring differs from processor resets and missing solenoid data

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Generic OBD-II
P06B9

Cylinder1 glow resistance is checked after basic electrical faults

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Generic OBD-II
P06BA

Cylinder2 performance can fail after an open-circuit check passes

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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.