sorry its messy...word should neaten it up... peter
ECU Codes Return to Technical The ECU in the car will log an error when there is a problem, determined by the data supplied by the various sensors in and around the engine. When an error is detected the "Check Engine" light will be turned on. Normally at this point Nissan would expect you to go to the dealer and have them correct the problem. However, this can be expensive and time consuming. There is an alternative. Using the procedures and tables of error codes below you can determine what caused your "Check Engine" light to turn on and possibly correct the problem. The methods below will explain how to access the ECU and check the codes. Accessing the ECU Accessing the ECU should be similar for both the B13 and B14 Sentras. The paragraph below pertains to accessing the ECU on a B14, but should help B13 owners as well. "Your ECU is located on the floor on the top of the hump between the drivers and passenger sides of the vehicle beneath the dash. There is a plastic cover over the ECU. You have to remove two nuts from the front (side towards the rear of the car) of the plastic cover. Don't drop them through the hole in the carpet like I did one. On each side (driver & passenger) there will be a plastic screw to remove. This will loosen the cover and the ECU. All of this is a pain in the BLEEP. The screw for resetting the computer is on the backside (towards the firewall) of the ECU on the passenger side of the vehicle. When you go to read/reset the computer there will be a plastic tape over the screw you will have to break. Just so you know the screw will turn easily and make sure you never force it. Also, don't get confused as to which way is right & left when your all twisted on the floor under the dash." - George A. Pandoff B13 Sentra (91-94) Retrieving the Codes To retrieve the codes from your car's ECU, do the following:
- With the engine off, turn the ignition to the ON setting.
- Turn the diagnostic mode selector on the back of the ECU fully clockwise.
- Wait two seconds and turn the mode selector fully counter clockwise. At this point the codes should begin to flash, and repeat.
To determine the code number use the following rules to decode the flashes: ? Long flashes (0.6 second) are the first digit ? Short flashes (0.3 second) are the last digit Example: A code of 12 would be 1 long flash and 2 short. A code of 55 would be 5 long and 5 short. Identifying the Codes Code Detected Items CA Models Non-CA Models Malfunction is detected when... Check Item
11* Crank angle sensor circuit X X ? Either 1º or 180º signal is not entered for the first few seconds during engine cranking. ? Either 1º or 180º signal is not input often enough while the engine speed is higher than the specified rpm. ? Harness and connector (If harness and connector are normal, replace crank angle sensor.) 12 Air flow meter circuit X X ? The air flow meter circuit is open or shorted. (An abnormally high or low voltage is entered.) ? Harness and connector (If harness and connector are normal, replace air flow meter.) 13 Engine temperature sensor circuit X X ? The engine temperature sensor circuit is open or shorted. (An abnormally higher or low output voltage is entered.) ? Harness and connector ? Engine temperature sensor 14 Vehicle speed sensor circuit X X ? The vehicle speed sensor circuit is open or shorted. ? Harness and connector ? Vehicle speed sensor (reed switch) 21* Ignition signal circuit X X ? The ignition signal in the primary circuit is not entered during engine cranking or running. ? Harness and connector ? Power transistor unit 31 ECU X X ? ECU calculation function is malfunctioning. ? Replace ECCS Control Unit (ECU) 32 EGR function X N/A ? EGR control valve does not operate. (EGR control valve spring does not lift.) ? EGR Control Valve ? EGR & Canister control solenoid valve 33 Exhaust gas temperature sensor circuit X X ? The exhaust gas sensor circuit is open or shorted. (An abnormally high or low output voltage is entered.) ? Harness and connector ? Exhaust gas sensor ? Fuel Pressure ? Injectors ? Intake air leaks 35 Exhaust gas temperature sensor circuit X N/A ? The exhaust gas temperature sensor circuit is open or shorted. (An abnormally high or low voltage is entered.) ? Harness and connector ? Exhaust gas temperature sensor 43 Throttle sensor circuit X X ? The throttle sensor circuit is open or shorted. (An abnormally high or low voltage is entered.) ? Harness and connector ? Throttle sensor 45 Injector leak X N/A ? Fuel leaks from injector. ? Injector 55 No malfunction in the above circuits X X *Check items causing a malfunction of crank angle sensor circuit first, if both code No. 11 and 21 are displayed at the same time. These items do not illuminate the check engine light. Source: 1991 Nissan Sentra/NX Coupe Service Manual