The check engine light came on, I read the codes U0420 and U0423. What are these codes?

The Check Engine light must be reset using an OBD-II code reader. Dealers have them as do repair shops. Places like AutoZone will read the codes for you, but normally will not reset the Check Engine light due to possible liability issues. You can purchase a code reader at these places to do this yourself. Make sure you get one that can read and reset the engine light. The very cheap ones cannot reset the Check Engine light.

using a real scan tool

if not you will miss most DTC errors.

use a real tool not just the silly dash bs VFD codes.

the dash is like the tip of an iceberg. see?

The easiest way to reset a check engine light on almost any modern car is to disconnect the battery wait five minutes and connect it back up. This will not tell you why the check engine light came on. For that you need a ODBII scanner, but if the issue was a gas cap left off and you have fixed that, then check engine the light should go off. I have found that many auto parts stores will read your car's ODBII codes for free.

Check engine light comes on and off, these are indication that there is some error code stored in your vehicles ECM. The engine module computer needs to be scanned. These will give the code and as per the error code the further problem can be detected and confirmed. The engine light indicator blinks or remains steady on dash when engine computer noticed any problem with any engine electrically operated components.

For more help, I suggest you to refer the help links provided below. These will let you know more about which areas to look, check, when there is engine light coming up on dash panel.

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Click the link below: -------

Check Engine Light Reset Procedure?

http://whoisbyme.blogspot.in/2012/06/check-engine-light-reset-procedure.html

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Check Engine Light ON?

http://whoisbyme.blogspot.in/2012/06/check-engine-light-on.html

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Intermittent Check Engine Light?

http://whoisbyme.blogspot.in/2012/06/intermittent-check-engine-light.html

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WHY Check Engine Light On car?

http://schematicsdiagram.blogspot.com/2011/06/check-engine-light-on-car.html

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Check Engine Light, VSC light and Traction Control Light ON?

http://whoisbyme.blogspot.com/2012/06/check-engine-lightvsc-light-and.html

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Check engine light flashing?

http://technoanswers.blogspot.in/2012/02/check-engine-light-flashing.html

Service engine soon Light Turned OFF after Jump Start?

http://whatisbyme.blogspot.in/2012/06/service-engine-soon-light-turned-off.html

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After replacing throttle body the Check engine light starts blinking?

http://technoanswers.blogspot.com/2012/01/after-replacing-throttle-body-check.html

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2005 Chevy Impala: Service Vehicle Soon Warning Light?

http://whoisbyme.blogspot.in/2012/06/2005-chevy-impala-service-vehicle-soon.html

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Malfunction Indicator Light ON

http://whoisbyme.blogspot.in/2012/06/malfunction-indicator-light-on.html

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Check power-train message with orange engine light came on?

http://howtobyme.blogspot.in/2012/02/check-power-train-message-with-orange.html

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2007 Toyota Highlander Hybrid: Yellow Check Engine Light ON dash?

http://whatisbyme.blogspot.in/2012/05/2007-toyota-highlander-hybrid-yellow.html

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1999 Toyota Tacoma: Check Engine Light Read Code P0171?

http://whatisbyme.blogspot.in/2012/05/1999-toyota-tacoma-check-engine-light.html

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Car Runs Fine But Check Engine light is ON?

http://whatisbyme.blogspot.in/2012/05/car-runs-fine-but-check-engine-light-is.html

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Check engine light with codes P2195 and P2197?

http://howtobyme.blogspot.in/2012/01/check-engine-light-with-codes-p2195-and.html

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How to Read Codes from Check Engine Light?

http://schematicsdiagram.blogspot.com/2011/12/how-to-read-codes-from-check-engine.html

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Vehicle smog test failed Due to NO MIL/check engine light?

http://schematicsdiagram.blogspot.com/2011/12/vehicle-smog-test-failed-due-to-no.html

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OBD Code is cleared but check engine light will not RESET?

http://schematicsdiagram.blogspot.in/2012/02/obd-code-is-cleared-but-check-engine.html

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Car jerks while going uphill and Check engine light is ON?

http://schematicsdiagram.blogspot.com/2011/12/car-jerks-while-going-uphill-and-check.html

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Toyota Camry Check engine light flashes while driving?

http://schematicsdiagram.blogspot.in/2012/02/toyota-camry-check-engine-light-flashes.html

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These details will help.

Thanks.

Hi

When any vehicle engine light comes on it generates a code, that code is read by a diagnostic tool that reads identifies and displays the code(s), to indicate the problem the senors have detected.


Codes can be reset to recheck if the fault is genuine or not, but without the tool its difficult to determine the cause of the engine light appearing.


Read the manufacturers suggestions or call a garage for a diagnostic quote.


cheers

go to O-Reilly's Auto Parts and ask for them to read the check engine codes for you.

VSC and TRAC lights will come on any time the check engine light does to reduce engine load. As such these lights being on may have nothing to do with the why the check engine light came on.

If the check engine light is on, a trouble code(s) has been stored in the computer that points to the problem area. The dealer should have read this code(s) to come up with what was wrong. Did the dealer give you a sheet with the trouble code number on it?

The engine may have variable valve timing, if it is not working the engine will revert back to a fail safe condition so that no damage will occur. But it will not be running a peak performance. Or it could be something with the engine timing system.

If you want to do your own checking, start calling autoparts stores to see if one will read the trouble codes for free, it is an easy job. AutoZone will read codes for free.

Hope this help.

BMW engine light

Comes on if DME engine management system self diagnostic fault detected. Will stay on until codes are called up and memory erased.

With OBD read the code as follows. Turn on ignition key, press accelerator pedal to the floor five times within 5 seconds. The check engine light will remain on for 5 sec , blik off, come on for 2,5 sec, go off for 2,5 sec and fault code will begin to flash. If more than one fault exist 2nd fault code will be separated by 2,5 sec pause. after fault codes there will be a 0.5 sec flash and light will remain off. to read codes again do procedure again.

Canceling of codes. make sure fault code is present (short blink and light goes out for long period), depress throttle pedal for at least 10 sec. read fault codes again and check for code 1444 (no faults stored.)

Check also the following, fuel pump, oxygen sensor, fuel injectors, engine coolant temp sensor, idle speed control valve, mass airflow sensor and too many other things.

Manufacturer Specific Codes

P1100 BARO Sensor Circuit - Read Our Article on Automotive Circuit Testing For Help With This Toyota Check Engine Light Code

P1120 Accelerator Pedal Position Sensor Circuit - Read Our Article on Automotive Circuit Testing For Help With This Toyota Check Engine Light Code

P1121 Accelerator Pedal Position Sensor Range/Performance Problem

P1125 Throttle Control Motor Circuit - Read Our Article on Automotive Circuit Testing For Help With This Toyota Check Engine Light Code

P1126 Magnetic Clutch Circuit

P1127 ETCS Actuator Power Source Circuit

P1128 Throttle Control Motor Lock

P1129 Electric Throttle Control System

P1130 Air/Fuel Sensor Circuit Range/Performance (Bank 1 Sensor 1) - Read Our Article On Oxygen Sensor Codes For Help With This Toyota Check Engine Light Code - More Related Information

P1133 Air/Fuel Sensor Circuit Response (Bank 1 Sensor 1) - Read Our Article On Oxygen Sensor Codes For Help With This Toyota Check Engine Light Code

P1135 Air/Fuel Sensor Heater Circuit Response (Bank 1 Sensor 1) - Read Our Article On Oxygen Sensor Codes For Help With This Toyota Check Engine Light Code - More Related Information

P1150 Air/Fuel Sensor Circuit Range/Performance (Bank 1 Sensor 2)

P1153 Air/Fuel Sensor Circuit Response (Bank 1 Sensor 2) - Read Our Article On Oxygen Sensor Codes For Help With This Toyota Check Engine Light Code

P1155 Air/Fuel Sensor Heater Circuit. (Bank 1 Sensor 2)

P1200 Fuel Pump Relay Circuit

P1300 Igniter Circuit Malfunction - No. 1

P1305 Igniter Circuit Malfunction - No. 2

P1335 No Crankshaft Position Sensor Signal - Engine Running

P1349 VVT System

P1400 Sub-Throttle Position Sensor

P1401 Sub-Throttle Position Sensor Range/Performance Problem

P1405 Turbo Pressure Sensor Circuit

P1406 Turbo Pressure Sensor Range/Performance Problem

P1410 EGR Valve Position Sensor Circuit Malfunction - Read Our Article on EGR Valve Codes For Help With This Toyota Check Engine Light Code

P1411 EGR Valve Position Sensor Circuit Range/Performance - Read Our Article on EGR Valve Codes For Help With This Toyota Check Engine Light Code

P1500 Starter Signal Circuit

P1510 Boost Pressure Control Circuit

P1511 Boost Pressure Low

P1512 Boost Pressure High

P1520 Stop Lamp Switch Signal Malfunction

P1565 Cruise Control Main Switch Circuit

P1600 ECM BATT Malfunction

P1605 Knock Control CPU

P1630 Traction Control System

P1633 ECM

P1652 Idle Air Control Valve Control Circuit

P1656 OCV Circuit

P1658 Wastegate Valve Control Circuit

P1661 EGR Circuit

P1662 EGR Bypass Valve Control Circuit

P1700 Vehicle Speed Sensor '2' Circuit Fault

P1705 Direct Clutch Speed Circuit Fault

P1765 Linear Shift Solenoid Circuit Fault

P1780 Park/Neutral Position Switch Malfunction (Only For A/T)

Back To Top Of Toyota Check Engine Light Codes Page

Engine-light-help.com

P1100 Induction Control Motor Position Sensor Fault

P1101 Traction Control Vacuum Solenoid Circuit Fault - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1102 Traction Control Ventilation Solenoid Circuit Fault - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1103 Turbocharger Wastegate Actuator

P1104 Turbocharger Wastegate Solenoid

P1105 Fuel Pressure Solenoid

P1294 Target Idle Speed Not Reached

P1295 No 5 Volt Supply To TP Sensor

P1296 No 5 Volt Supply To MAP Sensor

P1297 No Charge In MAP From Start To Run

P1300 Ignition Timing Adjustment Circuit - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1390 Timing Belt Skipped One Tooth Or More

P1391 Intermittent Loss Of CMP Or CKP Sensor Signals - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1400 Manifold Differential Pressure Sensor Circuit - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1443 EVAP Purge Control Solenoid '2' Circuit Fault

P1486 EVAP Leak Monitor Pinched Hose Detected

P1487 High Speed Radiator Fan Control Relay Circuit Fault - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1489 High Speed Condenser Fan Control Relay Fault - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1490 Low Speed Fan Control Relay Fault

P1492 Battery Temperature Sensor High Voltage

P1494 EVAP Ventilation Switch Or Mechanical Fault

P1495 EVAP Ventilation Solenoid Circuit Fault

P1496 5 Volt Supply Output Too Low

P1500 Alternator FR Terminal Circuit - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1600 Serial Communication Link

P1696 PCM Failure EEPROM Write Denied

P1698 No CCD Messages From TCM

P1715 Pulse Generator Assembly

P1750 Solenoid Assembly

P1791 PCM ECT Level Signal To TCM Circuit Fault

P1899 P/N Position/Transaxle Range Switch Circuit Fault - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1751 A/T Control Relay

P1791 Engine Coolant Temperature Level Input Circuit - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code

P1795 Throttle Position Input Circuit To TCM - Read Our Article On Automotive Circuit Testing For Help With This Mitsubishi Check Engine Light Code