Car RPM not reading at Smog Check

Maintenance/Repairs
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1

Hi
I recently went to have my car smogged here in San Jose, CA. At the first shop i went to the guy said that his machine wasn’t pick up the rpms so he couldn’t do the smog check. He said it might be the machine and to come back later. Later i came back, same result, so he said try another shop. I go to the other shop…strike 3.
I asked the guy at the second shop why he couldn’t just take the rpm reading like they do on previous model years from the distributor, and he said, “blah blah blah visual inspection, blah some kind of excuse” i wasn’t really listening.

The tach on the dash is reading the rpms fine. I have no CEL and the car runs smoothly, gets good mileage, and no weird noises.
So is there an easy-intermediate DIY fix for this?

2

@SanJoseKei‌

What year is this car?

Does your car even have a distributor?

If it’s 1996 or newer, it’s OBD2. In that case, the rpm information should be available to the smog station equipment when the guy hooks up to your car’s data link connector

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@db4690‌
Thanks for the reply. Sorry. Yes it’s 1996, and it has an ignition coil, not a distributor.
Both places hooked up the car to the datalink connector and that wasn’t, for whatever reason, reading the RPM signal.

4

BTW not sure if it’s relevant the car is a manual transmission.

5

This: http://pinoutsguide.com/CarElectronics/bmw_obd_ii_diagnostic_pinout.shtml
says that the RPM signal comes through the DLC (data link connector) on pin #9. Apparently someone should inspect the DLC wiring, especially that specific wire.

6

I just recalled something

When I was working at the Benz dealer, we became aware that some 1996 models were supposedly OBD2 compliant, yet there were some problems when the guy at the smog station hooked up his equipment.

This had less to do with Benz specifically and more to do with the fact that some of the europeans didn’t exactly populate the DLC the same way as the domestics. I wouldn’t be too surprised if BMW also made the same “mistake” in the early days of OBD2

By the way . . . this isn’t a Canadian and/or gray market car, is it?

7

@db4690‌
Thanks for the reply. Do you happen to recall what the resolution was for the Benz? The VIN starts WBA so this car was made in Munich. The car was originally purchased in Cali so pretty sure it’s not Grey/canadian market.

@cigroller‌ Thanks for the pinout link! I’ll check at home if i get a signal on 9

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For Benz, the resolution was to provide the smog technicians with a technical service bulletin . . . which explained the “discrepancies” . . . so that they wouldn’t categorically flunk the cars

Come to think of it, CARB also issued their own bulletins. Their monthly newsletters keeps the technicians up to date, as to which cars have which “discrepancies”