Lexus - Toyota OBD1 Diagnostic Trouble Code

Area

Open in E1(ground) circuit
* Check, clean, tighten all ground connections.

Open in injector circuit
* Test the circuit from the ECM connector checking for values specified in factory service manual.

Fuel pump failing. Unable to keep up with demand.

Fuel injectors clogged or poor pattern

Open or short in upstream oxygen sensor circuit

Upstream oxygen sensor
* Aftermarket sensor
* Sensor vent clogged with mud

Ignition system

Engine coolant temperature sensor
* ECM thinks engine is warm then uses O2 sensor before hot and ready

Volume air flow meter (AFM)
* Repeatedly poke the gate to ensure that it never sticks
* Test the AFM using service manual procedures.

Vacuum leak
* Cracked lines
* Valve cover beather filter
* Brake Booster
* Aftermarket intake tube

Engine Control Module(ECM)

Exhaust leak (misleading sensor)

Fuel filter clogged

EGR stuck open or leaking
* VSV or wiring to it faulty

Throttle Position Sensor(TPS) faulty or out of adjustment

Diagnosis

Oxygen sensor output is less than 0.45 V for at least 90 seconds when oxygen sensor is warmed up (racing at 2.000 rpm) and drive at 50 – 100 km/h

When the engine speed varies by more than 15 rpm over the preceding crankshaft position period during a period of 50 seconds during idling with the engine coolant temperature 75’C (167’F) or more.

Tips

The first troubleshooting step should be to verify that the engine is in fact running lean. It is possible for a malfunction to cause a misleading diagnostic code. One example is that an exhaust leak will introduce outside oxygen that the ECM will interpret as a lean condition. The ECM will respond by continually increasing fuel delivery creating a rich condition while the code will be lean. Examine the spark plugs and observe/smell the exhaust to verify that the engine is running lean.

Use the YODA OBD1 to monitor oxygen sensor, target fuel trim, injector pulse, TPS idle switch, TPS value, air measurement and coolant temperature.