303-14A Electronic Engine Controls- 4.0L: Description And Operation (page 20 of 28)

UHEGO/HEGO and MAF/IAT Sensor 

There are several adaptive maps associated with the fuelling strategy. Within the fuelling strategy the ECM calculates 
short-term adaptions and long term adaptions. The ECM will monitor the deterioration of the HO2S over a period of time. 
It will also monitor the current correction associated with the sensors. 
 
The ECM will store a fault code in circumstances where an adaption is forced to exceed its operating parameters. At the 
same time, the ECM will record the engine speed, engine load and intake air temperature. 
 

CKP Sensor 

The characteristics of the signal supplied by the CKP sensor are learned by the ECM. This enables the ECM to set an 
adaption and support the engine misfire detection function. Due to the small variation between different flywheels and 
different CKP sensors, the adaption must be reset if either component is renewed, or removed and refitted. It is also 
necessary to reset the flywheel adaption if the ECM is renewed or replaced. The ECM supports four flywheel adaptions 
for the CKP sensor. Each adaption relates to a specific engine speed range. The engine speed ranges are detailed in the 
table below: 
 

Misfire Detection 

Legislation requires that the ECM must be able to detect the presence of an engine misfire. It must be able to detect 
misfires at two separate levels. The first level is a misfire that could lead to the vehicle emissions exceeding 1.5 times the 
Federal Test Procedure (FTP) requirements for the engine. The second level is a misfire that may cause catalyst damage.
 
The ECM monitors the number of misfire occurrences within two engine speed ranges. If the ECM detects more than a 
predetermined number of misfire occurrences within either of these two ranges, over two consecutive journeys, the ECM 
will record a fault code and details of the engine speed, engine load and engine coolant temperature. In addition, the ECM 
monitors the number of misfire occurrences that happen in a 'window' of 200 engine revolutions. The misfire occurrences 
are assigned a weighting according to their likely impact on the catalysts. If the number of misfires exceeds a certain 
value, the ECM stores catalyst-damaging fault codes, along with the engine speed, engine load and engine coolant 
temperature. 
 
The signal from the crankshaft position sensor indicates how fast the poles on the flywheel are passing the sensor tip. A 
sine wave is generated each time a pole passes the sensor tip. The ECM can detect variations in flywheel speed by 
monitoring the sine wave signal supplied by the crankshaft position sensor. 
 
By assessing this signal, the ECM can detect the presence of an engine misfire. At this time, the ECM will assess the 
amount of variation in the signal received from the crankshaft position sensor and assigns a roughness value to it. This 
roughness value can be viewed within the real time monitoring feature, using T4. The ECM will evaluate the signal 
against a number of factors and will decide whether to count the occurrence or ignore it. The ECM can assign a 
roughness and misfire signal for each cylinder, (i.e. identify which cylinder is misfiring). 
 

T4 Diagnostics 

The ECM stores faults as Diagnostic Trouble Codes (DTC), referred to as 'P' codes. The 'P' codes are defined by OBD 
legislation and, together with their associated environmental and freeze frame data, can be read using a third party scan 
tool or T4. T4 can also read real time data from each sensor, the adaptive values currently being employed and the 
current fuelling, ignition and idle settings. 
 

Adaptions  Engine Speed, rev/min 

1 

1800 - 3000 

2 

3001 - 3800 

3 

3801 - 4600 

4 

4601 - 5400 

P Code No 

Component/ Signal 

Fault Description 

P0011 

CMP/CKP/VVT 

Bank A CMP/CKP Position error high , VVT retard position