So I have a check engine light that randomly.

1993 E36

MEMBER
1993 BMW 325I
25,300 MILES

So I have a check engine light that randomly pops on. The code that pops up is 1221. This indicates bad signal from O2. Well I replaced the O2 with a factory unit. And it still randomly pulls the 1221 code. What else could cause this?

Wednesday, April 3rd, 2013 AT 3:51 PM

1 Reply

WRENCHTECH

MECHANIC
20,757 POSTS

If a code 1221 or 1222 is present, cancel the DME fault code memory after noting all other existing codes.
Start the engine and warm it up to normal operating temperature. Drive the vehicle varying the load conditions. If the "Check Engine" light does not illuminate the problem is intermittent. If the "Check Engine" light does illuminate and a fault code 1221 or 1222 is present continue with step 3.
With the ignition switch in the OFF position, disconnect the oxygen sensor in-line connector X6200.
Turn the ignition switch to the run position and make the following voltage measurements at connector (male half).

Black wire (terminal 2), and ground = approx. 0.65 volts.
Black wire (terminal 2), and yellow wire (terminal 1) = approx. 0.45 volts.

Turn the ignition switch OFF and measure between:

Black wire (terminal 2), and yellow wire (terminal 1) = 0 volts.
If all voltages are correct, continue with step 6.
If any voltages are incorrect, check wires to terminals of the DME control unit harness connector (disconnected), for an open or short to ground. If the wires are OK, the DME control unit is defective.

Check the following items for operation and repair or replace as necessary. If no problems are found continue with step 7.

RUNNING RICH

Engine oil diluted with fuel
Operation of the purge valve
Operation of the charcoal canister
Operation of the DME main relay
Operation of the fuel pump relay
Stuck open injectors
Operation of the of the fuel pressure regulator

RUNNING LEAN

Air leak at crankcase vent hose
Air leak at the idle control valve hoses
Air leak at the rubber boot between the air flow meter and throttle housing
Air leak at injector rubber sealing rings
Clogged injectors
Insufficient fuel pressure
Bad fuel (water in fuel)

With the ignition switch OFF, install a new oxygen sensor (known good unit).
Reconnect harness connectors, start the engine, and warm it up to normal operating temperature. Drive the vehicle varying the load conditions. If the "Check Engine" light does not illuminate, retain the new oxygen sensor. If the "Check Engine" light does illuminate and a fault code 1221 or 1222 is present the DME control unit is defective.