Citroen AX fault codes

From Haynes Automotive Engine Management and Fuel Injection Systems Manual (3344)
Page 19.16 Fault code table (Citroen and Peugeot)
Code Item 11 End of diagnosis
12 Initiation of diagnosis 13x ATS 14x CTS 21x TPS 22 Stepper motor 27x VSS 31x Lambda control 41 CAS 42 Injector or fuel pump control 51 OS 52 Lambda control 53x Battery voltage 54 ECM
x Faults that typically will cause the ECM to enter LOS (limited operating strategy) and use a default value in place of the sensor.
To obtain fault codes short the green lead side of the Fault Code Reader (FCR) multi-plug to earth for 4 seconds with the ignition on while an assistant watches the fault lamp on the dashboard (or use two long lengths of cable). The FCR is situated by the o/s headlamp.
My 1994 Citroen AX had a running problem. The Electronic Control Module (ECM) was unable to read the Coolant Temperature Sensor (CTS) giving fault code 14. The CTS was replaced to no avail. The ECM substitutes a default value which makes the engine run badly. The problem was a poor connection on pin 25 of the multi-plug (P 19.14 - the lead in the illustration is on the wrong end of the plug). The middle row starts at pin 20 from the lead end. (Check for continuity between pin 25 and the CTS first.) Removing and replacing the plug would cure the problem and remove the fault code temporarily. I eventually cured the problem by cutting the lead to pin 25 and soldering a permanent connection to the male pin on the ECM.
If the Throttle Potentiometer (TPS) wears out (mine did at 50,000), a replacement is around 300 quid (possibly cheaper in France). The manufacturing cost is probably no more than a pound. I wrote to the Consumers Association but they weren't interested. If you're buying second hand check the fault codes first. Take the vehicle for a run first in case the owner has cleared the fault codes from the memory of the ECM!
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