Deceleration Enleanment Mode - Excuse me, is enleanment a real word?...

Every time the engine decelerates the fuel injection pulse width is reduced and sometimes even cut-off. This is to prevent backfires and engine manifold flooding. See how it all works here.



Deceleration enleanment or fuel cut-off mode is reached during periods of deceleration. In this mode, the ECM simply reduces injector pulse width or momentarily shuts the injectors off in order to reduce high emissions and engine backfire. The main signal inputs to the ECM for this mode are the TPS, RPM and the VSS (vehicle speed sensor). This is the reason why a faulty TPS signal that shorts to ground intermittently can send the system into fuel cutoff mode, creating a drivability concern. And, during this condition the ECM reacts as a closed throttle deceleration condition. Another common fault relating to this mode is in systems with an idle switch, whereby, the idle air bypass screw is set too high and the engine idles up-and-down between 900 and 1500 RPM. The reason for this is simply that the ECM is receiving a closed throttle signal (from the idle switch) and the idle speed is raising above normal, causing the ECM to cut injector pulse (injector cut-off mode). To solve this problem, adjust the idle air bypass screw, unless there is large vacuum leak, in which case repairing the vacuum leak will solve the problem. Once the TPS or idle switch signals the ECM of a closed throttle or idle condition and the RPM has dropped bellow a preset value, the system goes into idle-mode. There are other possible reasons why an ECM would activate the fuel cut off mode. For example If the engine were to reach a pre-programmed high engine speed (high RPM), the ECM would cut injector pulse to protect the engine from damage. Also, if the vehicle reaches a pre-determined high speed, for safety reasons, some systems would momentarily cut fuel and ignition to protect the driver from damage. The last two conditions vary from one manufacturer to another. The other sensors associated with this mode. An erratic VSS signal, for instance, may send the system into fuel cut-off, since the ECM perceives the vehicle speed as being dangerously high. The last possible condition for fuel cut off is one that happens all the time. Whenever the ignition switch is turned off, the ECM stops all injector and ignition pulses. Some possible related faults are power feed circuits that stay on even after the key has turned off. Two very common examples are improperly connected aftermarket alarm systems that feed power to the ECM causing the engine to diesel after shut off or whenever the cooling fan is routed directly to power all the time. In this last case, the cooling fan motor act as a power generator (from the spinning momentum of the blade) even after the power has been cut-off, causing the engine to keep running for a few seconds after ignition key shut-off. The self-generated power from the spinning fan motor also feeds the ECM, making it unable to enter fuel cut-off mode in order for it to properly shut down.



Hit Counter

Ask DIY-Car-Doctor

Watch our Videos

More Services


Sensors                 O2-Sensor                  APP-Sensor                CAM-Sensor               CRK-Sensor               ECT-Sensor               IAT-Sensor                 Knock-Sensor              MAF-Sensor                MAP-Sensor                TPS-Sensor                 VSS-Sensor                FRP-Sensor                AFR-Sensor              

Actuators               Fuel-Injectors            Ignition-Coil           Leak-Detection Pump  GM-Series Alternator   Idle-Control Valve      EGR-System            EVAP-System      

Repair Strategies Current-Ramping      Lack of Power           Fuel-Flow Volume     Ignition Waveform       Ignition Testing          A/F Ratio Diagnosis    Minimum Air Rate      No Fuel-Pressure       No Injector Pulse      No-Start/No-Spark     General No-Start      

ECM/PCM Modes Cranking Enrichment   Warm-up Cycle         Open-Loop            Closed-Loop            Accel. Enrichment Deceleration Leaning   Idle Control             Low-Voltage Correction Clear Flood Mode     Selective Inj. Cut-Off   Limp-In Mode           Exhaust Variable Valve

 OBD-2 Codes

Generic DTCs            GM Cars DTCs           GM Truck DTCs        Ford DTCs                  Ford Trucks DTCs        Dodge DTCs                BMW DTCs                 Honda/Acura DTCs       Hyundai DTCs              Isuzu DTCs                  Jaguar DTCs                Kia DTCs                     Land Rover DTCs          Mazda DTCs                Mercedes DTCs           Mitsubishi DTCs           Nissan/Infinity DTCs     Saab DTCs                  Subaru DTCs               Toyota DTCs                Volvo DTCs                  VW/Audi DTCs        

 Code Setting Criteria

Dodge CSC                 Ford CSC                    GM CSC                     Honda/Acura CSC        Hyundai CSC               Isuzu CSC                   Kia CSC                      Mazda CSC                 Mitsubishi CSC            Nissan/Infinity CSC      Subaru CSC                Toyota/Lexus CSC

SRS Airbag DTC

GM SRS Airbag Code   GM Truck SRS Code    Ford SRS Airbag Code  Ford Truck SRS Code   Dodge SRS Code        Dodge Truck SRS Code Acura/Honda SRS Code Isuzu SRS Codes         Mazda SRS Codes        Subaru SRS Codes Infinity/Nissan SRS       Kia SRS Codes     Hyundai SRS Codes     Mitsubishi SRS Codes Lexus/Toyota SRS

How to Get SRS Codes

Retrieving Dodge SRS   Retrieving Ford SRS     Retrieving GM SRS      Retrieving Honda SRS   Hyundai/Kia/Mitsu SRS Isuzu/Mazda/Subaru     Retrieving Toyota SRS  Nissan/Infinity SRS

SRS-Airbag Repair Guide

Deleting SRS Codes   Dodge SRS Location       Dodge SRS Operation     Ford SRS Location          Ford SRS Operation        GM SRS Location            GM SRS Operation           Honda SRS Location       Honda SRS Operation     Isuzu/Mazda/Suba Loc.   Isuzu/Mazda/Suba Ope Kia/Hyun/Mitsu Location Kia/Hyun/Mitsu Oper.       Nissan/Infinity Location   Nissan/Infinity Operation Toyota/Lexus Location    Toyota/Lexus Operation 


copyright 2011 Mandy Concepcion, Automotive Diagnostics and Publishing