Malfunction Indicator Lamp (MIL) trouble codes may be stored in the ECM and are related to areas of the PGM-FI (programmed fuel injection system), idle control, fuel supply, intake are, or emission controls. The MIL is also commonly known as a Check Engine Light (CEL).

When the TCM senses an abnormality in the input or output system, the D4 indicator lamp in the gauge may blink. D4 trouble codes are generally automatic transmission related. However, as noted in Section 14-48 of the service manual, some PGM-FI problems will make the D4 indicator light come on...”

When you jump the Service Check Connector (SCS), it may blink a trouble code for the MIL or D4 lamp, respectively. The trouble codes for the MIL and D4 lamp have different meaning.

Sometimes the D4 and the Malfunction Indicator Lamp (MIL) may come on simultaneously. If so, check the number of blinks on the MIL, then reset the memory by removing the BACK-UP fuse (7.5A fuse) in the under hood fuse/relay box for more than 10 seconds. Drive the vehicle for several minutes at over 30 mph and recheck the MIL. (Refer to section 14-51 of the service manual)

Since the MIL did not blink a trouble code and the D4 did blink a trouble code, you would diagnose the transmission related trouble code. In your case, a transmission related trouble code 14. Trouble codes are also known as a Diagnostic Trouble Codes (DTCs).

As noted in the service manual (Section 11-19), “If the SCS short connector is connected and there are no DTCs stored in the ECM, the MIL will stay on.”

So the short recap is, based on the above and what you said there are currently no stored trouble code in the ECM.

 

Well, it looks like my ECU was in Back-Up mode (BU) after all ... and I can see why. Time for some board-level repair.

Edits:
- Added pic of board back (looks fine). I have Hi-Res pics, but they won't fit here.
- I also opened TCU. Passes visual inspection. Re-sealed.

 

Sometimes there may be a short somewhere that can damage the ECU components. For example, a short at some sensor wiring which feeds into the ECU.

 

This is about as clean as I dare ... board is 20 years old. The chemicals that leaked out of the capacitor corroded the traces but they are actually in pretty good shape. Of course, some of the protective trace paint came off. Both sides of the board have a thick clear rubberized coating. It likely saved the board, but makes it difficult to do trace/part continuity checks.

C17 is Nichicon PR(M) 33uf-35v-105c. The cap. reads bad on the ESR Checker (ESR=2.80 - Cap=28.6). Plus, the chemicals have to stay INSIDE the cap to work.

Instead of making a lot of posts, I think I'll try to just edit these last 2 as I make progress.

- All ECU traces pass continuity checks with ohm meter. I'll do another pass after repair.
- I don't have the exact replacement cap in my shop, so I'll go by the electronics supply house tomorrow morning and get the right part.
- While computers removed, I check BWN/WHT wire for continuity (as decribed further along in D4-14 FlowChart). Passed.
- I replaced cap. Had to use Nichicon PW(M) 47uf-50v-105c (ESR=0.43 - Cap=53.0). Even if you can find a 33uf, I still recommend a 50v.
- Re-installed computers. Car still works. No errors or DTC after starting car.
- Tip: Remember to reconnect computer cables before re-mounting to metal shield/holder (just reverse dis-assembly steps).
- No CEL/MIL/D4 dash lights after 3 drive cycles. Did some high-speed and stop&go driving. Looking good so far.

 

Quote from my 94 Accord Shop Manual (should be in yours also).

"If the MIL is on when the engine is running, connect the SCS service connector to the service check connector. If no code is displayed (MIL stays on steady), the back-up system is in operation. "

I've had two ECM failures on my 94 EX, and close examination of both boards revealed no indication of damage.

good luck

 

Interesting. In 19 years, I've ever seen D4 flash or even a CEL/MIL light at all for that matter ... then this. It has been a great car.

 

Well, I installed a new cap., re-assembled, and drove car 3 times (pretty fast and hard ... total of 15 miles). All ok so far.

It was kinda intermittent ... so only time will tell (more "drive cycles").

See edits above.

 

I can confirm that after a full reset of all computers, and before you start the engine, you still get a steady MIL light when you short the SCC.

To have an indication (steady on MIL) that means both:
1. Back-Up (BU) system in operation ... BAD
2. No errors or DTC present ... GOOD

... is confusing to say the least. Thank goodness OBD2 came along eventually.

If it wasn't for the TCU error (D4-Code14) FlowChart sending me to check the ECU (PGM-FI) ... I would likely have never found the problem.

 

thanks for posting your fix.

good luck

 

The new capacitor definitely fixed the ECU (PGM-FI) computer. No more MIL/CEL error code flashing (or jumping into "limp-along-mode" ) in over a month and in these conditions ...

- Driving car almost every day
- Highway speeds (70 mph +)
- Long trips across town
- 90-100f temp days

Thanks again everyone ... not only for the messages, but also for leading me to the educational materials that helped me identify and fix the problem.

This repair is note-worthy ... a $0.50 part (the cap) soldered into one of the computers ... keeping the whole car (engine) from working properly.