1994 855T A7 error code 123

azureblue · Post by **azureblue** » 07 Feb 2015, 10:27

Which I think is "Digital output 48 pulse short to 12V supply"..
uh, wat? I assume this means there is a short somewhere in the trip computer circuitry, but does anyone know where I could begin tracing it down and fixing it?

Thanks....

Post by **Juan62** » 08 Feb 2015, 09:16

Sounds like temperature sensor unit is faulty. See picture and go to IPDUSA (dot) com for more info and then research for others for pricing.

azureblue · Post by **azureblue** » 08 Feb 2015, 11:27

this appears to be an engine temp sensor,and I don't think the trip computer handles that input..... IIRC, A7 codes are just for the trip computer.

Post by **Ozark Lee** » 08 Feb 2015, 15:26

Did you try to just clear it? It may be an old stored code.

...Lee

azureblue · Post by **azureblue** » 08 Feb 2015, 19:34

No - it's been about 6 months since I pulled the battery out. I should clear, or disconnect the battery, and see if it comes back..

Post by **Ozark Lee** » 08 Feb 2015, 20:57

Go ahead and clear it with the A/B boxes, then you know it is cleared. Disconnecting the battery doesn't always clear the error codes.

...Lee

azureblue · Post by **azureblue** » 09 Feb 2015, 09:30

Thanks- I didn't know that. Much appreciated..

Post by **esl_97_850_T5** » 11 Feb 2015, 08:45

azureblue,

I presume you solved your problem by clearing the DTC with the A/B boxes like Lee advised, but for yours and others info...

1. More correctly stated, A7 codes are for the combined instrument panel. It's true that the trip computer communicates with the combined instrument panel (COMBI) ECU. But the term "trip computer" is not synonymous with "combined instrument panel" or "COMBI".

It's true that the trip computer does not receive the engine coolant temp.

However, the COMBI does receive the engine coolant temp, and the A7 (ie, COMBI) codes can indicate an engine coolant temp related problem. The problem can originate with the actual engine coolant temp sensor, or it can originate in the wiring from the sensor to the engine ECU, or in the wiring from the engine ECU to the COMBI.

The A7 codes 1-2-1 and 1-2-2 are the two examples of engine coolant temp related problems in 1995 (and prior) 850s.

2. As you correctly inferred, your A7 code 1-2-3 relates to the 48-pulse signal (not the coolant temp). The 1-2-3 code in "instrument panel.pdf" in the 1995 Volvo 850 Service Manual is listed as "Incorrect 48-Pulse Signal" in the "INSTRUMENT CLUSTER DIAGNOSTIC FAULT CODES TABLE (1995)" table, and that table says to see "SPEEDOMETER TEST", which then explains that this A7 1-2-3 problem can arise from:

- a faulty Vehicle Speed Sensor (VSS) which comes from the transmission in the 1995 850 (and presumably azureblue's 1994 850 also),

- an open circuit in Yellow/Brown wire between instrument cluster 30-pin connector terminal No. 3 and VSS connector terminal No. 1,

- a faulty instrument cluster,

- incorrect VSS mounting,

- an open circuit in Green/Yellow wire between VSS connector terminal No. 2 and instrument cluster 30-pin connector terminal No. 2, or

- an open ground in circuit between instrument cluster 30-pin connector terminal No. 15 (Brown wire) and ground.

For a 1994 850, its best to focus in "instrument panel.pdf" on the A7-oriented "1-2-3" stuff rather than the 1996-oriented "CI-123" stuff.

esl_97_850_T5

azureblue · Post by **azureblue** » 11 Feb 2015, 09:44

Thanks for the information. No, due to the latest version (R2015.4.2) of the flu, I have not been able to sort this out..

I am going to bank on a bad 30 pin connector connection. The engine temp gauge is reading normal, and the engine comes up to "normal" as it should, and it doesn't appear the engine is getting too hot. It's been years since I pulled the cluster to replace bulbs in the display, so maybe I didn't seat the connector properly. As soon as this bug passes....

BTW, if there are any of us around Winston Salem, NC, the local pick a part has a huge selection of 850 and newer Volvos there.... And they just got in an XC today.