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Reading ECU Trouble Codes - Code Breakers

How To Read Your ECU Trouble Code

Reading ECU trouble codes can cut trouble-shooting time in half. Just like in the block-buster hit "U-571," when Matthew and the rest of his daring American crew had to steal the Germans code reading machine named "Enigma." With this, the Americans were able to decipher codes sent out by the enemy to put an end to the secrecy. In the fuel injection world, deciphering electronic code is the first step to eliminate the nasty check engine light. Understanding the code can also pinpoint the precise area of malfunction.

So how can I own my own "Enigma" machine you ask? For most cars, it doesn't require breaking into a car dealer to steal the "Enigma" equivalent, all you need is this issue of Import Tuner. As a fair warning, this is only the first step in troubleshooting your car, but it is the biggest step to problem-solving the needs of your Toyota, Honda/Acura, Mitsubishi, Nissan or Mazda.

For the above applications, the rule below will apply for most of the manufacturers we will discuss-don't make me repeat myself. Deciphering codes requires reading the light sequences. With the car in the "ON" position, the light can emit a few different types of flashes. If the light starts out with a long extended flash, this means digits of 10. (Example: one long flash would mean 10) If the light blinks rapidly immediately after, these would be considered digits of one (Example: five flashes would represent 5). Putting our two sets of flashes together, we would end up with the number 15. By referring to our chart for Hondas, we would find our problem is in the ignition system.

If there is a pause between flashes, then it's on to the next code. For example, if there is a long pause between our first two numbers then our first code will be code 15 and our second set of numbers would be our next code.

Honda/Acura 88-'91 Honda; '86-'93 AcuraThese models are by far the easiest to read. The ECUs are equipped with a window on the topside of the computer. On the other side of the window is Honda's "Enigma" machine-well, more like an LED (Light-Emitting-Diode). This little LED holds the key to unlocking the codes to understanding why the damned engine light is on. Simply put, the car in the "ON"-position; watch for the flashing sequence on the LED.

'92-'00 Honda; '94-'00 AcuraAn upgrade from the early-model Hondas, this ECU no longer has the access windows with an LED. Replacing the LED is a flashing check engine light. All that is needed to pull trouble codes is a jumper wire. Locate the factory diagnostic plug located next to the ECU for Integras and Civics or by the center console for Preludes and some Acuras. A two-pin connector contains a brown and black wire. Jump the two wires together and put the vehicle in the "ON" position.

ToyotaToyota is pretty standard with reading code. Most of the trouble codes apply to a majority of its line of cars. Locating the diagnostic plug will give access to pulling your trouble codes. This is found in the engine bay of the vehicle. By using a jumper wire, connect pin E1 and T1 or TE1 (Some vehicles will have pin TE1 instead of T1) and put the vehicle in the "ON"-position. Make sure that all accessories are off and the vehicle is in neutral.

One difference of reading Toyota's code is rather than long pulses to represent digits of 10, Toyota uses short pulses to represent the first digit and uses short pulses again to represent the second digit in a two-digit number. If a vehicle has more than one code, there will be a two-second pause between flashes. This signifies that a new code is going to be revealed. If a repeated code comes up, this signifies that the string of code is starting again.

NissanNissan vehicles require accessing the factory ECU. These ECUs can be placed in five different types of diagnostic modes. For checking trouble codes, the ECU needs to be put into Mode II (Self-diagnostic results). The ECU contains a dial (potentiometer) on the side of the case. This can be accessed by unbolting the ECU, making sure the factory wiring harness is still connected. Place the vehicle in the "ON" position and turn the dial fully clockwise with a flat head screwdriver, wait 2 seconds, then turn the dial back fully counter clockwise. At this time, the check engine light should reveal the vehicle's status. Some of the ECUs will also contain a red LED that will also give flash sequences just like the check engine light. If your Nissan has a green and red LED, the sequences will read as green for digits of 10 and red for digits of one.

MazdaJust like Toyotas, most Mazdas require locating the diagnostic plug beneath the hood and jumping the required pins. Reading the code is just like reading a code from a Honda. Before pulling any codes, make sure the vehicle is in the "OFF" position. The vehicle we tested was a '95 RX-7 but most late-model Mazdas require jumping the same pins in the diagnostic plug. Most Mazdas will apply to this sequence but to be certain check your service manual. Our RX-7 required jumping the "TEN" pin and ground (GND) and placing the car in the "ON" position. Codes are signified through the check engine light on the dash and new codes begin within 4 seconds from the last code.

MitsubishiUnlike most of the cars explained in this story, Mitsubishis require more than just a jumper wire and a check engine light. This vehicle requires use of a multi-meter. The meter will act as your jumper wire within the diagnostic plug. The diagnostic plug is located on the right-hand side of the fuse box and the two pins that will need to be jumped with the meter are the number 12 and 1 pins. With the meter on the voltage setting and the car in the "ON" position, the code could be read in short and long bursts of voltage sent across the meter. Long bursts of voltage spikes signify digits of 10 and short spikes represent digits of one. Codes can be read with a digital volt/ohm meter but an analog meter is much easier to read.

Honda engine codes
0 ECU
1 Oxygen Content
3 Map sensor
5 Map sensor
6 Crank Angle
7 Throttle Angle
8 TDC position
9 No 1 Cylinder Position
63 Intake Air Temperature
12 Exhaust Gas Recirculation System
13 Atmosphere Pressure
14 Electronic Air Control
15 Ignition Output Signal
16 Fuel Injector
17 Vehicle Speed Sensor
20 Electronic Load Detector
22 VTEC System Malfunction
23 Knock Sensor
41 O2 Sensor Heater
43 Fuel Supply System
45 System Too Rich or To Lean
48 Primary Heated O2 Sensor
54 Crankshaft Speed Fluctuation Sensor
61 Primary O2 Sensor Circuit
63 Secondary O2 Sensor Circuit
67 Catalyst System
70 Automatic Transaxle
71-74 Random Misfire
80 Exhaust Gas Recirculation
86 Engine Coolant Temperature Circuit
90 Evaporative Emission Control System Leak Detected
91 Fuel Tank Pressure Circuit
92 Evaporative Emission Control System Insufficient
Some trouble codes are not listed for certain models and some codes apply to only California-legal vehicles.
Mazda engine codes
2 Crank Angle Sensor (NE Signal)
3 Crank Angle Sensor (G Signal)
5 Knock Signal
6 Speedometer Signal
9 Water Temp Sensor
11 Intake Air Temp Sensor
12 Throttle Angle Sensor
13 Pressure Sensor
14 Atmospheric Sensor
15 O2 Sensor
16 EGR Switch
17 Feedback System
18 Throttle Sensor (Narrow Range)
20, 26, 27 & 37 Metering Oil Pump Position Sensor
23 Fuel Thermosensor
25 Solenoid Valve (Pressure Regulator Control)
28 Solenoid Valve (EGR)
30 Solenoid Valve (Split Air Bypass)
31 Solenoid Valve (Relief 1)
32 Solenoid Valve (Switching)
33 Solenoid Valve (Port Air Bypass)
34 Solenoid Valve (Idle Speed Control)
38 Solenoid Valve (Acceleration Warm Up System)
39 Solenoid Valve (Relief 2)
40 Solenoid Valve (Purge control)
42 Solenoid Valve (Turbo Pre Control)
43 Solenoid Valve (Wastegate Control)
44 Solenoid Valve (Turbo Control)
45 Solenoid Valve (Charge Control)
46 Solenoid Valve (Charge Relief)
50 Solenoid Valve (Double Throttle Control)
51 Fuel Pump Relay
54 Air Pump Relay
71, 73 Injector
76 Slip Lock Up Off Signal
77 Torque Reduced Signal
Some trouble codes are not listed for certain models and some codes apply to only California cars.
Toyota engine codes
12 RPM Signal
13 PRM Signal
14 Ignition Signal
21 O2 Sensor Signal
22 Water Temp Signal
24 Intake Air Temp Sensor Signal
25 Air Fuel Ratio Lean
26 Air Fuel Ratio Rich
27 Sub-Oxygen Sensor Signal
31 Vacuum Sensor Signal
32 Air Flow Meter Signal
34 Turbocharging Pressure Signal
35 Turbocharging Pressure Sensor Signal
41 Throttle Position Sensor Signal
42 Vehicle Speed Sensor Signal
43 Starter Signal
51 Switch Condition Signal
52 Knock Sensor Signal
53 Knock Control Signal in ECU
71 EGR Malfunction
Some trouble codes are not listed for certain models and some codes apply to only California cars.
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Mitsubishi engine codes
11 O2 Sensor
12 Volume Air Flow Sensor
13 Intake Air temperature Sensor
14 Throttle Position Sensor
21 Engine Coolant Temp Sensor
22 Crankshaft Position Sensor
23 Camshaft Position Sensor
24 Vehicle Speed Sensor
25 Barometric Pressure Sensor
31 Knock Sensor
41 Injector
42 Fuel Pump
43 EGR
44 Ignition Coil/Ignition power transistor unit
Some trouble codes are not listed for certain models and some codes apply to only California cars.
Nissan engine codes
12 RPM Signal
11 Crank Angle Circuit
12 Air Flow Meter Circuit
13 Engine Temperature Sensor Circuit
14 Vehicle Speed Sensor Circuit
21 Ignition Signal Missing In Primary Coil
31 ECU
32 EGR Function
33 Exhaust Gas Sensor Circuit
34 Knock Sensor Circuit
35 Exhaust Gas Temperature Sensor Circuit
43 Throttle Sensor Circuit
45 Injector Leak
55 No Malfunction In The Above Circuits
Some trouble codes are not listed for certain models and some codes apply to only California cars.
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