J Squared
02-25-2008, 03:38 AM
Nissan was thoughtful enough to provide most factory ECUs with built-in diagnostics, even before OBDII was standard. In fact, I believe even OBDII ECUs still have the OBDI diagnostics function built in, alongside the standard check port. You can use the ECU itself to check for issues, which is helpful if you have performed a swap and did not bother with the OBDII port.
Running diagnostics on the ECU can help a ton when troubleshooting issues or trying to track down power loss or bad gas mileage. It will let you know when a sensor is bad, whether the engine is seeing any knock, or if you have a clogged cat. Some even have built-in A/F metering (although i wouldnt trust it so much...). Steps for checking the ECU codes are below:
First things first, gain access to the ECU. It is usually located in the (U.S.) passenger side kick panel. You will probably have to unbolt the ECU from the unibody to check the codes, as the diagnostics lights are almost always on the firewall side of the computer (why, I have no idea). Once you have full access to the ECU locate a recessed dial, located near a small oval opening in the side of the computer shell. The oval opening contains the code indicators, and the dial is used to set the diagnostics mode. It can also be used to fine-tune your idle, however that is unrelated to this process (give it a shot though, it works :) ). Make a mental note of where the dial sits currently, or perhaps mark the position on the ECU case. Next, rotate the Key to ON, and you are good to go for diagnostics.
Here is where the process gets a little more specific based on your ECU. Some Nissan ECUs have two LEDs in the oval for diagnostics, and some have one. Still others have none, and the CEL (check engine light) acts as the diagnostic light. To put the ECU into diagnostics mode if you have one (red) LED or no LEDs at all, simply turn the dial fully clockwise for two seconds, then turn it quickly back fully counter clockwise. The codes will show up (either on the LED or the car's CEL) as a two digit number, represented by flashes on the light. You will see a series of long flashes (approximately two seconds), followed by a series of short flashes (one second); this is the returned code. It is possible to get multiple codes one after another so pay close attention to the flashes, and perhaps jot them down. Here is an example:
long - long - long - short - short (pause) long - short - short - short
This would be codes 32 and 13, or EGR and ECT sensors.
If you have one red and one green LED you are in luck as the separate LEDs are a bit easier to read. However, this type of ECU has multiple diagnostic modes, and you will have to set the ECU to the correct mode first. To do so, rotate the dial on the ECU fully clockwise until the red LED starts flashing. The flashes, seperated by pauses, indicate which mode is current. Wait for the LED to flash three times in quick succession, then immediately rotate the dial completely counter clockwise. Mode three is the diagnostics mode.
Wait a moment, and the LEDs will begin to display any codes stored in the ECU. The red LED indicates the first digit, the green the second digit. Again, multiple codes may come up, so pay attention. Naturally:
red - red - red - red - green - green - green - green - green
would indicate a code 45, or a leaky injector.
Below is a list of codes that may be returned. Keep in mind that a code should ALWAYS be returned, even if everything is OK (represented by code 55). If no codes are returned after waiting for 10-15 seconds, start the process over. Also, to stop the diagnostics mode simply turn the key OFF and return the dial to its original position. You can also return codes while the car is running, and I would definitely recommend this as some codes will not come up if the car is only turned on. Still, friends dont let friends troubleshoot and drive; ask a buddy for help :)
11 Crank Angle Sensor
12 Mass Air Flow Sensor
13 ECT Sensor
14 Vehicle Speed Sensor
16 TCS Signal
21 Ignition Signal Circuit
25 Idle Air Control Valve
22 Fuel Pump Control
31 ECM
32 EGR Function
33 Heated Oxygen Sensor
34 Knock Sensor
35 EGR Temperature Sensor (RH)
41 Intake Air Temperature Sensor
42 Fuel Pump Sensor
43 Throttle Position Sensor
45 Injector Leak
46 Secondary Throttle Sensor
51 Injector Analysis
53 Exhaust Gas Sensor (LH)
54 Signal Circuit From A/T Control Unit To ECM
55 System OK
65-71 Single Cylinder Or Multiple Cylinder Misfire
72 Three Way catalyst Function
76 Fuel Injection System Function
77 Rear Heated Oxygen Sensor
82 Crankshaft Position Sensor
84 A/T Diagnosis Communication Line
91 Front Heated Oxygen Sensor Heater
103 Park/Neutral Position Switch
105 EGR & Canister Control Solenoid
Running diagnostics on the ECU can help a ton when troubleshooting issues or trying to track down power loss or bad gas mileage. It will let you know when a sensor is bad, whether the engine is seeing any knock, or if you have a clogged cat. Some even have built-in A/F metering (although i wouldnt trust it so much...). Steps for checking the ECU codes are below:
First things first, gain access to the ECU. It is usually located in the (U.S.) passenger side kick panel. You will probably have to unbolt the ECU from the unibody to check the codes, as the diagnostics lights are almost always on the firewall side of the computer (why, I have no idea). Once you have full access to the ECU locate a recessed dial, located near a small oval opening in the side of the computer shell. The oval opening contains the code indicators, and the dial is used to set the diagnostics mode. It can also be used to fine-tune your idle, however that is unrelated to this process (give it a shot though, it works :) ). Make a mental note of where the dial sits currently, or perhaps mark the position on the ECU case. Next, rotate the Key to ON, and you are good to go for diagnostics.
Here is where the process gets a little more specific based on your ECU. Some Nissan ECUs have two LEDs in the oval for diagnostics, and some have one. Still others have none, and the CEL (check engine light) acts as the diagnostic light. To put the ECU into diagnostics mode if you have one (red) LED or no LEDs at all, simply turn the dial fully clockwise for two seconds, then turn it quickly back fully counter clockwise. The codes will show up (either on the LED or the car's CEL) as a two digit number, represented by flashes on the light. You will see a series of long flashes (approximately two seconds), followed by a series of short flashes (one second); this is the returned code. It is possible to get multiple codes one after another so pay close attention to the flashes, and perhaps jot them down. Here is an example:
long - long - long - short - short (pause) long - short - short - short
This would be codes 32 and 13, or EGR and ECT sensors.
If you have one red and one green LED you are in luck as the separate LEDs are a bit easier to read. However, this type of ECU has multiple diagnostic modes, and you will have to set the ECU to the correct mode first. To do so, rotate the dial on the ECU fully clockwise until the red LED starts flashing. The flashes, seperated by pauses, indicate which mode is current. Wait for the LED to flash three times in quick succession, then immediately rotate the dial completely counter clockwise. Mode three is the diagnostics mode.
Wait a moment, and the LEDs will begin to display any codes stored in the ECU. The red LED indicates the first digit, the green the second digit. Again, multiple codes may come up, so pay attention. Naturally:
red - red - red - red - green - green - green - green - green
would indicate a code 45, or a leaky injector.
Below is a list of codes that may be returned. Keep in mind that a code should ALWAYS be returned, even if everything is OK (represented by code 55). If no codes are returned after waiting for 10-15 seconds, start the process over. Also, to stop the diagnostics mode simply turn the key OFF and return the dial to its original position. You can also return codes while the car is running, and I would definitely recommend this as some codes will not come up if the car is only turned on. Still, friends dont let friends troubleshoot and drive; ask a buddy for help :)
11 Crank Angle Sensor
12 Mass Air Flow Sensor
13 ECT Sensor
14 Vehicle Speed Sensor
16 TCS Signal
21 Ignition Signal Circuit
25 Idle Air Control Valve
22 Fuel Pump Control
31 ECM
32 EGR Function
33 Heated Oxygen Sensor
34 Knock Sensor
35 EGR Temperature Sensor (RH)
41 Intake Air Temperature Sensor
42 Fuel Pump Sensor
43 Throttle Position Sensor
45 Injector Leak
46 Secondary Throttle Sensor
51 Injector Analysis
53 Exhaust Gas Sensor (LH)
54 Signal Circuit From A/T Control Unit To ECM
55 System OK
65-71 Single Cylinder Or Multiple Cylinder Misfire
72 Three Way catalyst Function
76 Fuel Injection System Function
77 Rear Heated Oxygen Sensor
82 Crankshaft Position Sensor
84 A/T Diagnosis Communication Line
91 Front Heated Oxygen Sensor Heater
103 Park/Neutral Position Switch
105 EGR & Canister Control Solenoid