Lexus OBD1 Codes

Lexus OBD1 Codes Retrieval For Pre-1996 Vehicles
Lexus OBD1 Decoder
Lexus is the top end vehicle made by Toyota Corporation that first came out in 1990s. Diagnosing the meaning of the Lexus check engine light codes is basically the same way like most Toyota vehicles. To get the codes yourself, turn the engine off and connect a jumper wire between terminals TE1 and E1 of the diagnostic terminal connector located in the engine compartment or under the left side of the dash. Turning the engine key on but not starting the engine, the check engine light lamp in your dash panel will start to flash the codes. The codes are usually shown in 2 digits numbers like code 24 is 2 flashes, a pause and 4 flashes. A pause of 2.5 seconds will follow the next code. When all codes are transmitted, the entire code will be flashed again after 4.5 seconds. This process of getting Lexus OBD1 codes is the called the normal or regular test mode.

Lexus OBD Codes Reset
Resetting the codes is simple which is done by removing the fuse of the terminal EFI from junction box 2 for 10 seconds. Make sure to remove the jumper wire and switch the engine key off before clearing the codes.
Here are some popular Lexus vehicles 1990-1995 codes
Code 12 and Code 13 Rpm signal circuit fault
Code 14 Igniter signal circuit fault
Code 16 ECT control signal fault
Code 21 and Code 28 Main oxygen sensor fault (for ES300; SC300 & GS300 models)
Code 22 Coolant temperature circuit fault
Code 24 Intake temperature sensor circuit fault
Code 25 and Code 26 Air fuel ratio fault (for ES300 & SC300 models)
Code 27 Sub-oxygen sensor circuit fault (for ES300 CA & GS300 models)
Code 31 Low airflow meter voltage (for ES300 and GS300 models)
Code 32 High airflow meter voltage (for ES300 model)
Code 35 Barometric pressure sensor circuit fault (for GS300 & SC300 models)
Code 41 and Code 47 Throttle position sensor circuit fault
Code 42 Vehicle speed sensor circuit fault
Code 43 Starter signal
Code 51 Switch condition signal fault (for ES300; GS300 & SC300 models)
Code 52 Code 52 and Code 55 Knock sensor circuit fault
Code 71 EGR system circuit fault (for ES300; GS300 & SC300 models)
Code 78 Fuel pump control circuit fault (for GS300 & SC300 models)
Fixing Lexus OBD1 Codes
After getting your Lexus OBD1 codes, reset it first to confirm if you have a temporary or permanent hard codes. Temporary codes are usually erased whereas permanent hard codes need to be fixed before they can be erased. To erase, simply disconnect the battery negative terminal for 1-2 minutes and reconnect. Re-start engine until it is warmed up and get the code again. If you get the same code after the 2nd scanning, then that is called a permanent or hard failure code.
Hard Failures Code
Permanent or hard code is characterized when your check engine light in the dash remains on or it could flash repeatedly during engine operation. If it is caused by a sensor failure, the engine control module (ecm) will substitute another value to make the vehicle continue to run. At this condition called LIMP mode, the engine runs temporarily so it can be taken to a garage for repairs.
Intermittent Failures Code
This temporary code can cause the check engine light to flicker until the problem goes away. This condition occurs when if the code is not recorded in the ECM memory if it fails to appear in a certain time frame. This is caused by borderline defective sensor or poor wiring connections. Sometimes, intermittent codes will not show up during a regular warm up period but could sometime takes a day or two of driving before the code shows up. This is true if the defective component is borderline, meaning it could work 50-50 times during it's operation. Please take precaution when resetting the codes by disconnecting the battery.
Test Modes
This is the test used during road test if the regular diagnosis when the vehicle is parked will not work. To perform the test, use the same connection used in the regular test with the jumper wire connected making sure the jumper wire is hooked up when ignition key is off. Before road test, record the obd1 codes shown in the dash before doing the road test to simulate the vehicle problem. Once completed, record the fault codes shown in the dash. Take note that this TEST mode is more sensitive to intermittent codes because it also covers more circuits like starter signals, camshaft sensors, tps, AC and even neutral switch signals.
Lexus No Starts
When fixing Lexus no starts, you can begin by checking the starting system components like battery and it's connection; starter assembly and it's wiring and finally all the switches and relays associated with it. Getting the Lexus OBD1 codes helps because it narrows down the defective circuit instead of doing all the physical checks which is time consuming. In the end, fixing Lexus no starts will need both the practical way which needs individual component testing and electronic monitoring using OBD1 code detection. Shown below are two methods of fixing Lexus no starts by having the Lexus OBD1 codes and without.
1995 Lexus Es300 No Start with P0340 Code
A shop mechanic replaced the timing belt of the engine including front engine seals,and valve cover gaskets. Upon completion, the car was road tested and ran fine intially. A few minutes later the car quit and would hardly start. Later, it would only idle but died down completely after the throttle was opened up. Hooking up the scanner showed code P0340 camshaft sensor fault code (camshaft open short circuit) stored. When the code was reset, it just came back. The timing belt was replaced and including the camshaft sensor but it did not make any difference. It only make the engine idle rough ran but keeps cutting out with the same code.
CEL Advisor:
Most of this P0340 code can be fixed using dealer only (OEM) parts and if you happened to use aftermarket parts, replaced them. Next, make sure to align the timing belt properly during timing belt installation. Before installing the new cam sensor, look at the teeth of the camshaft pick up reluctor behind the engine gear cranshaft. This engine model is prone to breakage because the reluctor teeth becomes brittle when old and break off when disturbed. Double check this if possible and make sure all the readings to the camshaft sensor wirings are ok. If you can, you can compare camshaft readings to the ecm input terminals to verify if any of the camshaft wires are broken.
Final Fix
The engine fix was due to a couple of broken teeth off the relucter plate. The PCM could not read the TDC off the crankshaft with the broken teeth. This caused the camshatf sensor to be out of time with the crankshaft sensor causing it to set P0340 fault code. every time the engine would try to start.
1993 Lexus Es300 3.0L No Start No Code
This car had a transmission failure and it was replaced with a rebuilt one. All wirings were put back properly and transmission fluid changed including complete engine fluids replacements. After this, engine won't start. There was no spark or injector pulse. Checked cam and crank sensor wirings and reading looked OK with the voltmeter. There was no codes displayed in the dash when manually scanning. The ecm was finally replaced but it did not help.
Check Engine Light Advisor
Most transmission replacement requires that all wirings should be marked before removal so it can be put back during installation of the new transmission. If OK, go over the wiring diagram and check all ground and power supplies. Also check the presence of the computer (ecm) 5 volt refence in the main ecm terminals when the ignition is turn on. Do this also on the 5v on the sensor wiring connection to confirm continuity. Checking the 5v reading will guide you if the ecm is working or not.
Final Fix
Checking at the ecm terminals, the 5v presence was confirmed which is also available at the tps sensor connection. When checked at the mass sensor end, it showed zero volt. Replacing the mass sensor fixed the problem.

No comments:

Post a Comment