tachometer not working

[esl_97_850_T5]

Do you have a problem for which a Gauge Test would help in solving?
If so, what is it?
Is your tachometer not working, yet all other gauges are working?
Or are you simply trying to get A7 diagnostics working?

[michonsjm]

A7 does not work because it is a Yazaki cluster. Tach is only thing not working.

[esl_97_850_T5]

michonsjm,

1. If I were you and had a 1995 850 that had both the under-the-hood connector and the OBDII port, and the A7 port was not working, and my dash's tachometer was not working -- since I know how to do it -- I'd plug my ELM327 compatible device (that has at least ELM327 v1.4 functionality) into the OBDII port, turn ignition to pos II, then issue the following sequence:

ATZ
ATL1
ATE1
ATI
ATDP
ATSP 3
ATDP
ATH1
ATAL
ATKW0
ATTA 13
ATRA 13
ATIIA 51
ATWM 82 51 13 A1
ATSH 83 51 13
ATSI
AE01
B031
B231

[Now I'll switch out of the "if I were you" mode.]

If none of the commands/requests (ATZ thru B231) produce any response, then you are not connected to your ELM327 device. There's no point in going any further until you can get responses from the ELM327 AT commands.

If ATAL, ATKW0, ATTA 13, ATRA 13, ATIIA 51, ATWM 82 51 13 A1, ATSH 83 51 13 respond with something besides the ">" prompt (and possibly echoing themselves), yet do not all respond with OK, then there's no point in going any further, since your ELM327 device is not functionally equivalent to ELM327 v1.4 (or higher).

If your ATSI responds with "BUS INIT: BUS ERROR" or "BUS INIT: ...BUS ERROR", then check if your ignition is at pos II. If not, turn your ignition on, wait till the SRS warning sound stops, then issue the ATSI again.

If you ever get ATSI to respond with "BUS INIT: ...OK", then you can proceed with the AE01, B031, B231.

If most of your gauges swing through their ranges and the lights do their thing during the Gauge Test, then you know: a) you have a way to perform a COMBI Gauge Test, and b) your 1995's OBDII port is useful for something besides holding coins. The "...EE 01..." response to the AE01 request shows any existing COMBI DTCs. You can get that response interpreted at http://jonesrh.info/volvo850/kwpd3b0_interpreter.html.

2. As an alternative, you could also try reading the COMBI DTCs using a VAG/COM KKL cable with either Vol-FCR or Brick-Diag Free v0.0.6.6.

3. Regardless whether you do items 1 or 2 or not, and regardless whether either of them works or not, you might still consider some of the following ideas for diagnosing your "tach not working on 95 850 w/ Yazaki cluster" problem...

I assume you have a problem somewhere between the specific pin on the engine ECU (ECM)'s Connector B that sends the RPM signal to the COMBI and the specific COMBI pin that receives the RPM input signal from the ECM. Alternatively, it could be either one of those actual connection points -- either at the ECM or at the COMBI.

Where you look first probably depends on the exact nature of the tachometer failure. Does it always read 0? Does it always read some non-zero value? Is it intermittently flaky? Has it always happened while you owned the car? Did it begin after you made some repair? etc, etc.

The OTP Volvo 850 Repair Manual DVD has the ECM Connector B layout for several ECMs that might apply to 1995. That's where I'd obtain the proper pin # to measure from the ECM, if I had to go back in the circuit all the way to that point.

Might be a good idea to first take the instrument cluster out. By visual inspection, you might see something loose. Or you might be able to change the nature of the problem by wiggling one wire or another.

Both the downloadable Volvo_850.zip and its online HTML equivalent will have an instrument panel section that has a "TACHOMETER TEST" section. That might be mildly useful, but be aware that the ECM pin listed there might not be correct. Ideally, anything from the Volvo_850.zip should be verified with more specific info from the OTP Volvo 850 DVD -- both the "Parameter List" tables listing and describing the ECM pin #s and the actual wiring diagrams (preferably 1995 specific, or at least <= 1995 specific).

I question how useful the COMBI Yazaki document on the OTP Volvo 850 DVD would be to your 1995 850, since the only COMBI Yazaki document on the DVD is for the '98 S70/V70/C70. That being said, it still might be worth your while to glean whatever you can from it, since it has a wealth of diagnostic info. It does have a "Fault Symptoms / Checking Tachometer" section that has a small amount more info. And it has a highly useful breakdown of the 30 pins of the COMBI's 30-pin connector in the "Breakout Box and Parameter Tables / Signal Descriptions" section.

It looks like A11 is your end-point on the COMBI end of the suspect circuit.

esl_97_850_T5

[michonsjm]

Thanks for the write up. Tach worked until about 6 months ago. My son was driving it and said it started working intermittently then stopped completely. I took the cluster out and could not find any faults. Tried to measure voltage on the wire supplying the tach but was getting very low readings (low tenths of a volt). Not sure what the voltage should be. I think the 850.zip had a value but I didn't read anything close to it.