Diagnostic Article By Chris Rogers
 

Fault code reading on the 850 and 70 series classic shape cars also some 900 series.

Pre ’96 model year cars have a diagnostic unit behind the RH head lamp, this unit can be used by the owner to obtain flash fault codes from any ECU fitted to the car.
Diagnostic socket designations are as follows:

A1 = Auto transmission, A2 = Engine ECU or fuel system ECU on Jetronic cars.
A3 = ABS, A4 Battery +, A6, Ignition ECU Jetronic cars. A7 = Instruments
A8 = Ground
B1 = Electronic climate control, B2 = Cruise control, B5 = SRS (airbags) B6 = Power seats.
The method of use is documented well documented elsewhere.

Post ’96 cars were fitted with an OBDII style diagnostic socket on front of the gearlever under the coin holder marked OBDII. Most of the diagnostic access was changed to ISO 9141 style communications which means there is no access to the diagnostic information except by using a Volvo specific code reader or scan tool.
However some ECU’s in the later cars were the same as the earlier ones and can be read using a home made LED & switch code reader.

The ECU’s that can be read this way are as follows:

LH 3.2 Jetronic (Some 20V NA cars) Fuel ECU Pin 3, EZ-129K ignition ECU pin 1
Motronic 4.3, (T5 cars) Pin3
Fenix 5.2 10V cars) Pin 3
Electronic climate control, Pin 6
Cruise control, Pin 13
900 Series ABS Pin 12

Note: the fact that OBDII is marked on the coin holder cover does not guarantee the car is OBDII compliant.

OBDII is a US mandated (’96 on) OBD fault code reading system for emissions related diagnostics, it only covers engine ECU diagnostics and auto gearbox where an auto gearbox fault may affect emissions. It does not cover anything else for example ABS, airbags etc.

In the UK some 850 cars are OBDII compliant these are the late 2.5 20V NA, & 2.5 LPT cars fitted with Motronic 4.4 engine management systems. Every other petrol model is not OBDII compliant but can be read using ‘flash’ codes. Diesel cars are fitted with a Bosch MSA 15.7 ECU which an only be accessed using a Volvo specific code reader or scan tool.

70 series cars up to model year ’99 used a similar diagnostic system as the later 850 cars except that the only ECU that was flash code readable was the Fenix 5.2 system.
All pre ’99 70 series petrol cars fitted with the Motronic 4.4 engine management ECU are OBDII compliant. No diesel engine cars are OBDII compliant nor provide flash codes they require a Volvo dedicated code reader or scan tool for diagnostic access to them.

70 series cars ’99 on.
For ’99 the ECU system was changed again, petrol cars got the Motronic ME7 or Denso ECU’s and Diesels MSA 15.8.
Auto gearbox and ABS ECU’s where changed to fit in with the CANBUS system used. Diagnostic access for these ECU’s is via the CAN system.
The petrol cars are OBDII compliant but the diesels are not