Whenever the car is on, the check engine light is on. I'm running bareblock, so I'd figure that would have something to do with it... but it doesn't throw any codes.

What would cause the check engine light to STAY on, w/o throwing an engine code at all???

S5 GTU

 

Anyone? C'moooon! I need some help here! Actually, I'd guess it was from such low compression... but I'm just making sure.

 

^

 

Code 01 - Crank angle sensor
DCC1: S P .... (1 short light... long pause ... repeat),
DCC2: does not light.
Fail-safe mode: There is no fail-safe mode for this sensor.
Code 02 - Air flow meter.
DCC1: SS P ... (2 short lights... long pause ... repeat)
DCC2: does not light
Fail-safe mode: Maintains basic signal at preset level.

Code 03 - Water thermo sensor.
DCC1: SSS P .... (3 short lights... long pause ... repeat)
DCC2: does not light
Fail-safe mode: Maintains a constant 80 degree C command.
Comments: this is the two-wire sensor on the back of the thermostat housing

Code 04 - Intake air temp sensor.
DCC1: SSSS P .... (4 short lights... long pause ... repeat)
DCC2: does not light
Fail-safe mode: Maintains constant 20 degree C command.
Comments: This sensor is built into the air flow meter.

Code 05 - Oxygen (O2) sensor.
DCC1: L P.... (1 long light... long pause ... repeat)
DCC2: does not light
Fail-safe mode: The ECU stops feedback correction (open loop operation)
Comments: This sensor is located on the down-pipe / pre-cat.

Code 06 - Throttle sensor.
DCC1: LS P ... (1 long light ... 1 short light ... long pause ... repeat)
DCC2: does not light
Fail-safe mode: The ECU assumes 100% throttle position.
Comments: This is the TPS and it is located underneath the intercooler.

Code 07 - Boost/Pressure sensor.
DCC1: LSS P ... (1 long light ... 2 short lights ... long pause ... repeat)
DCC2: does not light
Fail-safe mode: Maintains constant command: 96 mm Hg (boost sensor), 26.3 kPa (pressure sensor)
Comments: This is located on the right shock tower.

Code 09 - Atmospheric Pressure sensor.
DCC1: LSSSS P ... (1 long light ... 4 short lights ... long pause ... repeat)
DCC2: does not light
Fail-safe mode: Maintains constant sea-level command (boost sensor)
Comments: This is located next to the ECU.

Code 12 - Trailing side coil failure.
DCC1: SS P ... (2 short lights ... long pause ... repeat)
DCC2: S P ... (1 short light ... long pause ... repeat)
Fail-safe mode: Stops operation of trailing side ignition
Comments: indicates a failure within the trailing side ignition system.

Code 15 - Intake air temperature sensor.
DCC1: L P ... (1 long light ... long pause ... repeat)
DCC2: S P ... (1 short light ... long pause ... repeat)
Fail-safe mode: Maintains constant 20C (68F) command.
Comments: This is located on the intake air pipe just prior to the throttle body.

Note: From our observations, it seems that if more than one error code exists, the ECU reports only the one of lower numeric value. If you have any information that support/refute this assumption please let us know so we can update the document.

 

try this

 

Is the check engine light on continuously when the green 1-pin check connector is grounded? If it is, than according to the Mazda FSM your ECU is defective and needs to be replaced.

Hot_Dog
90 GXL
02 RSX-S

 

just go over everything again. I found after my rebuild, it took me 2 months to get everything in order, ALL my idiot lights were on. oil leaks...blahblah.

I will say that the problem with my check engine light was grounds!! check all grounds, and check your tps... Then I got a microtech standalone and said FU#K YOU to my wiring harness and afm.

Just get a standalone and rip all that **** out





----------------------------------
89TII
Large Streetport
1100cc secondaries
Microtech EMS
Garret T04 H3
Lots O' Fuel

 

I'd say O2 sensor is the culprit. I am playing around with my '89 T2 right now and have a wide-band sensor in the exhaust. The narrow band sensor isn't in the car and the ECU is connected to nothing on the O2 line. I have no code and no engine light.

I also don't get to drive in closed loop very much as I drive to work on surface streets with a lot of stop/go traffic. I beleieve the stock ECU is very cautious about setting code 15 unless the wire is shorted to ground.

When I first bought the car the O2 was bad and after some extended freeway driving the check engine light would come on and the #15 code would be set.

Very odd....

 

Sorry, double post (gotta watch that back button!)

 

If the car is on and running, the check engine light is on. When I go to check the codes, there arn't any. The O2 sensor is brand new, and hooked up VERY well.

I plan to get some 10AWG wire, and make a few new grounds once I get my spare intake ported/beadblasted/whatnot. And if it's the ECU, I have a FOR SURE working one in the passanger seat of my Daily Beater

 

You might try unplugging the O2 sensor and see if it actually sets code 15 (O2 below 0.55v for 80sec after feedback system operation begins).

However, this is a funny statement as I'm not sure how feedback operation begins when there is no O2, so when does the 80 second timer start? If the timer doesn't start then how can the code be set?

I'm very disturbed that a check engine light can be displayed with no stored code on our cars. Typically it's the other way around. The ECU is storing 'pending' codes in memory without setting off the light. I see this on OBD-II cars all the time.