Cracking the Code: Toyota's Codes

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Cracking the Code: Toyota's Codes

Have you received diagnostic readers as gifts recently? 


These tiny devices attach to your vehicle’s diagnostic system, allowing you to get the service codes behind warning lights on your dashboard. While they don’t have the range and depth of the sophisticated diagnostics we use at A+ Japanese Auto Repair, they can give a clue about what’s going wrong in your vehicle and where to proceed. 


Understanding the problem is the beginning of finding an answer


It’s not enough to have the code. You will also need to understand what parts the code corresponds to and how the different codes in play work together. Our mechanics have years of diagnostic experience working this out. Although our mechanics can’t teach you which signifiers impact your car in a single scan of your diagnostic, we can teach you which codes your Toyota is most likely to encounter in a single check of your code reader:


P0171 - System Too Lean Fault

One of the most common trouble codes in V-6 and larger engines, P0171 is triggered by the first exhaust oxygen (02) sensor (aka upstream 02 sensor) on the “Bank 1” side of the engine. It denotes an imbalance in the oxygen of the fuel system, which can come from several different factors.


P0401 - EGR Flow Insufficient

The P0401 code demarks insufficient exhaust gas recirculation (or EGR flow), which helps to reduce combustion temperatures. A pinging or knocking is likely occurring when you get this code.


P0420 - P0429 - Catalyst System Efficiency Below Threshold Error

All P0420 - P0429 codes refer to the catalytic converter and exhaust system and fall into the general exhaust system code block. P0420 refers to the catalytic converter or - more specifically - the oxygen (O2) sensors before and after it on the bank 1 side of the exhaust system. This error might be Leaded fuel in an unleaded system, a failed catalytic converter, or even a failing O2 sensor or connection.


P0440 - EVAP Control System Malfunction

The P0440 code means that a disruption has occurred in the EVAP system. A faulty or leaking gas cap, or a plugged canister, most often triggers this code.

A failed purge solenoid.


P0441 - Evaporative Emission Control (EVAP) System Fault

The P0441 OBD-II code indicates an Evaporative Emission Control System Incorrect Purge Flow; in plain English, it’s noticing a bad vacuum switch or a leak in the EVAP system, which in turn is preventing fuel vapors from reaching the canister. When we encounter this code, we typically check the connection for the MAF, unplug and reconnect the MAF wiring harness, check the voltage of the MAF sensor, and replace r repair any faults found.


We hope this helps you understand the work ahead of a skilled mechanic when they see these codes on a Toyota. Remember that the investigation doesn’t end with a code; it begins with a code! 


Did You Know…?

Did you know that if your Toyota (or any other car we service) needs service and you don’t have time to bring it in, A+ Japanese Auto Repair offers a free pick-up and delivery service that can help you save time and energy?




Free Pickup & Delivery | Onsite Rental Vehicles | After Hours Pickup & Dropoff


At A+ Japanese Auto Repair, we pride ourselves on making your auto repair experience less stressful. When you need service for your vehicle, schedule an appointment today at A+ Japanese Auto Repair. We are conveniently located at 780 Industrial Road, San Carlos, CA 94070. 650-946-1856.

Categories: Toyota Service
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