Land Rover Brief To The New Diagnostic Standards A Rover Manual

							A brief guide to the new diagnostic standards  
 
Jaguar and Land Rover have adopted a new standard (ISO14229) for 
implementing there on board diagnostics that will provide more information to the 
Technician about a fault, DTC (Diagnostic Trouble Code). This guide will 
highlight the changes that the technician will see and what they mean in practice.   
Modules supporting this version of diagnostics will appear from 2004 MY 
onwards. 
Three byte DTCs  
DTCs (Diagnostic Trouble Codes) will now be three bytes long (except those 
obtained by Scan tool service which will still be two bytes hence the third byte 
from ECM will be 00 in most cases). The first two bytes will identify the fault area/ 
component and the third byte will be the fault type. (For example open circuit). 
The third byte fault type definitions are defined by SAE and are standard across 
all manufactures. The following example shows the make up of a typical DTC.   
 
P0720-14    Transmission Output Speed Sensor General Electrical Failure 
short circuit to ground or open circuit. Figure 1 
 
The WDS tester will decode the DTC fully.  
DTC Status  
In the background whenever the tester reads a DTC a fourth byte of data is 
retuned that contains information about the status of the DTC. This status 
information is decoded and displayed to the technician in two methods: 
 
Method 1 
By the chain link symbols on DTC monitor to indicate pending or Confirmed 
DTCs. 
 
Permanent  
Intermittent 
Pending 
Historic 
Unknown  No icon. 
ODST 
  
						

							Permanent.  Applied to a continuously monitored DTC which is logged (For 
example the results from t he associated on-board diagnostic test indicates that a 
fault exists) and where a co rresponding fault is currently present (For example 
was detected the last time the associat ed diagnostic test completed its run).  
 
Intermittent.  Applied to a continuously monitored DTC which is logged but where 
a corresponding fault is not currently pr esent (For example was not detected the 
last time the associated diagnostic test completed its run). 
 
Pending.   Applied to a continuously monitored (Emission-related) DTC which is 
explicitly reported as ‘pendi ng’ (For example a fault has  been detected in either 
the current or previous drive cycle, but  has not yet been present for the necessary 
complete drive cycle to enable it to  be transferred to the logged state). 
 
Historic. Applied to a continuously monitored  (Emission-related) DTC, which is 
explicitly reported as ‘histo ric’ (For example a previous ly detected fault which has 
not been detected fo r a set period). 
 
Unknown. Applied to a continuously monitored DTC, which is logged but does not 
fall into any of the previous categories (For exampl e the request for logged DTC’s 
was completed successfully, but the request for additional information was 
unsuccessful so that categorisation as  either Permanent or Intermittent was not 
possible). 
 
ODST.  Applied to an on-demand DTC that is  logged (For example as a result of 
running an on-demand self-test). 
 
  
						

							Figure 1 
 
 
Figure 2 shows full description of what is on the screen. 
 
Figure 2  
  
						

							Method 2 
The sorted ordering of the DTCs on the tester.  For example Not Tested  
 
The list of DTCs displayed with the status of Not Tested are DTCs for which the 
modules fault monitoring strategy has not yet been run. In order to have a 
particular DTC fault monitoring strategy run it will be necessary to perform an 
appropriate drive cycle for the DTC of interest. In many cases for power train 
items starting and running the engine for a short period of time can accomplish 
this.  
The aim of providing this information is to allow the technician to fix a fault and 
then check after a test drive that fixed DTCs is no longer in the Not Tested list 
nor in the failed list. The DTCs will not be displayed on WDS if it has been tested 
and passed by the module. 
 
Snapshot Records        
 
Snapshot records are similar in concept to the freeze frame data that is available 
for emissions related DTCs, but is supported for all DTCs under the new \
ISO 
14229 diagnostics.  If a module has several DTCs logged only some of them will 
have snapshot data available. A camera icon next to the DTC indicates the 
availability of snapshot data. If a DTC is highlighted that has snapshot data a 
camera tab will appear at the bottom of the screen. Under the camera tab the 
snapshot records will be displayed. (Figure 3). 
 
Figure 3 
  
						

							 
The snapshot record consists of the values a number of parameters when the 
snapshot was taken. For example vehicl e speed, temperature will be stored. The 
record number related to when the snapshot was taken For example record \
16 
(always supported) is stored  when the DTC is first confirmed as a failure and 
record 17 is when the DTC last failed.   
 
The first few modules with this function will only be able to support a limited 
amount of data e.g. X204 Electric Park Brake. The first vehicles to fully embrace 
the new standard will be Discovery 3 / LR3 and future Jaguar products. These 
new vehicles will fully support this functi onality with global data snapshot for all 
DTC’s that will include Odom eter reading, Engine running status, time and date 
stamp (relative to vehicle time For exam ple current time – time stamp = how long 
ago fault occurred.) In addition some will pr ovide additional local snapshot data 
For example. Engine speed when fault  occurred for Diesel ECM DTCs.