Service Indicator Reset

By wkohler, Mon Jul 16, 2007

Original thread: Service Indicator Reset

Problem: My "Oil Service" and/or "Inspection" lights are on.

Cause: Your car has "accumulated sufficient use" to set off the lights, which are designed to come on every 7,500 miles, alternating between "Oil Service" and "Inspection."

How to fix: Once you've carried out the procedures for either Oil Service or Inspection I or II as outlined in your Bentley manual in section 2, pages 6–10, you can reset the lights using the diagnostic connector in your motor compartment.

Motronic 1.1 cars have a 15-pin connector. Motronic 1.3 cars have a 20-pin connector:

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15-pin and 20-pin diagnostic connectors. Jump pins 1 and 7 to reset the service interval lights.

You can buy a tool that will do this for you. It costs about $50 and is a waste of money unless you aren't good with counting or watching your cluster. You could make a very similar tool using a 35mm film canister (who remembers those?) and a switch connected to two 6-foot wires inserted in the proper locations on the connector — it'll set you back about $3.00.

Reset procedure

To do it the cheapo way, get a paper clip. Bend it so it's straight, then bend it in half, creating a narrow "V" shape.

1. Jump pins 1 and 7 in the diagnostic connector. Pin positions are shown on the underside of the red cap, and they reflect the position of the pins when the cap is installed. The "V" shape helps maintain contact in the connector.
2. Get in the car. Turn the key to the second position (the one where all of the dash lights come on).
3. The Oil Service light should extinguish in 3–4 seconds. The Inspection light should extinguish in 8–11 seconds.
4. After your desired light has been extinguished, immediately turn the key to off. Failure to do so will result in an incorrect interval for the other light.
5. Remove the jumper, replace the cap, close the hood, and have a Dr. Pepper or a beer (if you're into that sort of thing).

What happens if my lights don't shut off?

If your lights don't shut off, or both are on, you have a problem Service Indicator (SI) board. The memory on the original board is stored using Ni-Cad batteries which have limited life and then start to corrode, leak, and just create a mess.

If this is the case, you can replace the board or bypass the on-board batteries and create a remote battery box of your own design. There are also battery-less boards that use flash memory.

Removing the instrument cluster

Removing the SI board might seem like a daunting task, but it's actually quite easy. I R&R'd mine in less than 20 minutes and had never pulled a cluster before.

1. Pull the steering wheel to the fully telescoped position.
2. Using a Phillips screwdriver, remove the two screws that hold the top of the cluster into the dash. Look below the top ridge of the dashboard. If your cluster has been out before, chances are they're missing. Be sure to celebrate that with a beer or a Dr. Pepper if that's the case.
3. Using a thin, rigid object (a putty knife is ideal), carefully pry between the plastic lip on the cluster and the dashboard. The cluster will pivot towards you.
4. Gently pull the cluster out of its home.
5. Not every wire has a separate connector, and everything is color coded. Carefully remove the connectors. The large rectangular connectors (blue, yellow, and white) each have a locking black component. Use a long, thin, flat-blade screwdriver to carefully release this locking component by working it straight out (it should only move 1/2" at most and stays connected to the connector).
6. The blue L-shaped connector pulls straight down (note its orientation before reassembly). This sends indicated speed from the speedometer to the cruise control. Failure to reattach this correctly will render cruise control inoperable.
7. If the car has ABS, the entire bulb and socket pull straight out of the cluster.
8. If the car is an automatic, a connector pulls straight back off the very bottom of the cluster (the PRND321 indicator). Carefully remove it.
9. All wires should now be free. If you're fortunate, you won't have to remove the wheel. Some owners have to because of clearance. Do not force anything. The most fragile part to watch is the automatic selector indicator board — it can get damaged on the top of the column.
10. If you have to remove the steering wheel: early cars (coarse-splined columns before 7/85) remove the horn button or center Roundel and use a 22mm socket to remove the nut. Mark the wheel relative to the column before you pull it. Later cars (after 7/85, fine-splined column) insert the key and turn to position 1 to deactivate the steering lock, then the rest is the same. Never try to remove the wheel using the steering lock as leverage — you can permanently damage the mechanism.
11. Remove the cluster and have a beer (or a Dr. Pepper).

"Installation is the reverse of removal." — Mr. Haynes

Replacing the SI board

Once you have the cluster out, go to a safe working environment with a clean, flat surface. Place the cluster face down on a towel and have a container for screws. This is a good time to inspect the odometer gears. Spare gears are available from Jeff Caplan at odometergears.com.

1. Remove the 8 screws that hold the cluster together with a Phillips screwdriver or an 8mm nut driver.
2. Separate the two halves (white and black). Ground yourself before handling the circuit boards.
3. Remove the speedometer. Pull straight out; do not wiggle it.

Early vs. late clusters: Early clusters have a separate SI board; late clusters include it on the main board. The easiest tell is the SI display: early clusters have 3 red LEDs, late clusters have 1. Use 4a for early, 4b for late.

4a. Early cluster (3 red LEDs)

Disconnect the green ribbon cable from the main board. Some clusters have a grounding wire from the SI board to the main board (a black wire with a sleeve connector over a pin on the main board); some don't. If it is connected, disconnect it carefully.

There are 3 small slotted screws that hold the SI board to the rear of the cluster. Remove them. If they have battery-acid buildup, soak them in baking soda and water to neutralize, then let them dry. The board lifts out. Neutralize any leaked acid around the board and let that dry too.

Install the new board (it is most likely green compared to the original yellow one — don't be alarmed) and reattach the 3 screws. Before attaching the ribbon cable and ground wire, make sure the two nuts holding the temp/fuel gauges to the main board are tight. If you were having issues with those gauges, they might not have been grounded properly. Reattach the ribbon cable and ground wire. Reassemble carefully; if something doesn't fit, don't force it.

You should have no leftover parts except the old board.

4b. Late cluster (1 red LED)

You are going to remove the main board of the instrument cluster and replace it. Remove all bulbs and the speedometer. Using a 10mm nut driver, remove the two nuts that secure the temperature/fuel gauges to the board. Affix those to the new board, replace all the bulbs, and reassemble.

Again, no leftover parts other than the old board.

Reinstall the cluster. Double-check all connections. Wait to lock the cluster in with the screws until you test-drive and confirm everything works. You may need to reset one or both lights afterward, but most likely not.

Remote battery box

Purchase a battery box for whichever cells you want to use. AA batteries are cheap, so that's what the PO of my car went with.

1. Remove the solder from the solder joints for the battery holder on the board (follow the (+) and (−) tabs through the board).
2. Solder a lead to each solder joint — be careful, there are other joints nearby. Do not solder to the tabs; that is what my car's PO did, and it failed pretty much by design.
3. Solder the leads to the terminals marked − and +. Ni-Cad batteries should be wired in series, but Li-Ion in parallel — you don't want more than 3 V, and Li-Ion cells do not come in lower voltage.
4. Find a place for the box that is easy to reach when the batteries need replacement, generally after 3–4 years depending on how harsh the environment is.