Hello, my 91 accord lx (180,000 miles) goes into limp mode (2nd and 3rd gears work) when the car is warm especially on hot days when I'm stuck in traffic. On a cool day (I live in Seattle so I mean temps in the 60s and below) if I'm moving the tranny will work fine. 3 years ago I had limp mode troubles and did the TCU capacitor/resistor replacement fix that's been talked about on this forum. That worked great. This time, I tried replacing some of the other resist/capac. in the lower right of the TCU circuit board and it didnt' help. I tried jumping the 2 pin connector that's behind the panel under the glove box. I got no codes. The s light comes on sometimes not every time. Two weeks ago when the s light was on as I pulled in the driveway, I jumped the connector and got 6 (I think). It was the code for the thermostatic sensor for the TCU. (I'd already tested the sensor and it read OK). So I went and bought a new one. No change. I just tested the thermoswitch sensor in boiling water. It tests ok. I've not tested the thermostat itself. I did start the motor with the radiator cap off and could not detect a flow in the water but the engine didn't overheat at idle. Top radiator hose was hot, lower hose warm. Oh, the fan didn't come on during or after when I did the idle test with the radiator cap off but like I said the engine didn't overheat.

I've been thinking that a fan is not coming on while running causing the heating problems in stop and go traffic. The fan does come on when I stop the car. So if I stop at say the autoparts store, when I come out in 10 minutes the car starts off fine. Once stopped in traffic or whatever, it's back to limp mode.

Any advice on how to come at this problem would be great. Thanks.

 

Code 6 for TCU is fault in shift position console switch wire circuit. Symptoms are failure to shift other than 2-4, LockUp clutch does not engage or engages/disengages alternately.

You appear to be confused about ECU (engine control unit) and TCU (trans control unit) codes. They are separate and have different fault problems.

Suggest downloading a manual from Online Manuals post in DIY forum for guidance.

Turn AC on and keyswitch to On. Both cooling fans should come on and run. If not, either fan/s are faulty or thermoswitch A (on thermostat housing) is faulty.

good luck

 

Thanks Texas Honda. I should've done better homework re talking about codes. I downloaded the manual. It opens as 100+ separate PDFs. Is that right? (I'm using a Mac but could load it on a PC). Noob question: do service manuals have trouble shooting guides?

I forgot to mention that I've been using the troubleshooting info from http://techauto.awardspace.com to try to come at this problem.

I just turned the AC on and keyswitch on at the same time. Both fans came on.

 

Yes, service manual has extensive diagnostics for TCU error codes. Yes, my 91 manual is same arrangement of many pdf files. Not as handy as some but useable. Find the index and print that page to allow referencing the other file numbers more easily.

You can jumper thermoswitch A on the thermostat housing to confirm fans coming on w/o AC on. If fans don't come on when temp reaches about middle range, the thermoswitch A may not be working correctly. If they do come on, then overheating may be result of failed thermostat.

Referenced link is a good source, but service manual has additional info.

good luck

 

Thanks TexasHonda. I jumped thermoswitch A w/o AC on. The fan came on.

To clarify, when I jumped the 2 pin connector behind the right kick panel, it was the check engine light that blinked 6 times indicating a water temperature sensor malfunction according to the ECU diagnostic trouble codes. I replaced the sensor even though my multi tester had shown it to be w/in spec. No change.

When I tested thermoswich A in boiling water, I got no readings when cold to about 180 degrees, then I got 2.4 ohms until the water boiled, then I got no readings again.

I know it goes against the "diagnose first, then replace" credo but I'm tempted to replace both thermoswitch A and the thermostat too.I've owned the car for 14 years and am pretty sure neither has ever been replaced and I've been trying to diagnose this hummer over the course of multiple weekends. In contrast to my smug feelings after I fixed the burnt out resistors and capacitors in the TCU a few years ago, this go round with tranny limp mode troubles is much less satisfying. If you have any more suggestions, I'd appreciate hearing them. I'll post the results of replacing the parts I mentioned in any case. Thanks again.

 

Here's the troubleshooting guide for ECU code 6:
ECU Code 6 Troubleshooting

 

Thermoswitch A should not close until 194F and resistance (if zero'd VOM) should be very close to zero. If it's really 2.4 ohms, that could be a problem causing a voltage loss to the fans.

See Fan Controls in Electrical section of shop manual.

Measure electrical resistance of thermister (coolant temp sensor) at engine and again at ECM connector. If approx. same value is obtained, the ECM is likely fault.

good luck

 

Thanks redbull-1 and TexasHonda. I've not hauled off and bought parts yet. I'm still trying to diagnose. I'll re-post when I get somewhere.

Accronyms: VOM- voltage meter?; ECU - engine control unit, ECM? (=ecu?)

 

VOM=volt ohm meter

ECU = Engine Control Unit = ECM = Engine Control Module = Engine Computer

 

And the TCU code 6 is for the gear position switch. That code does not cause the S light to flash when driving.