Farmall 70A - DTC 3157 (Resolved)

[klancf51]

Farmall 70A no start – ADIC (Analog Digital Instrument Cluster) displayed “Stop Sign” icon and DTC 3157. Also, once, briefly displayed DTC 14901. The tractor had been sitting outside for about 10 days.

DTC 3157 - ECU Not Detected on CAN bus.
DTC 14901 – ECU not present​

• We visually inspected the main wiring harness from the ECU back to the ADIC .
• We disconnected the wiring harness connectors from the ECU and re-connected them.
• We jump started the tractor successfully. After disconnecting the jumper cables, it ran for a few minutes and shut down with DTC 3157.
• We charged the battery. Again, it started and ran for a few minutes and shut down with DTC 3157.
• The next morning. we removed the battery, put it on the charger; meanwhile sprayed the grounding bolts in the battery compartment with brake cleaner and tightened them. Battery ground cable was not fully secure to frame and tightened ~ 1/8 turn. Re-installed the charged battery. Afterwards, tractor started and ran normally.

The reason we were suspicious of the battery and grounding is that for most ECU-related issues, the Farmall 70A Service Manual suggests “faulty supply voltage or ground, missing” as the #1 failure mode. The reason is that not all units on the CAN bus switch off communication at the same voltage level. This creates the situation where some components or control units are trying to communicate with switched-off units. Key takeaway: Always verify a properly charged battery and charging system as the first step in troubleshooting a CAN bus comms issue.

Btw, the DTC codes listed in the Farmall 70A Service Manual do not numerically correspond with those displayed on the ADIC. The Service Manual uses hexadecimal codes AND they don't convert directly to the DTCs on the ADIC. CASE IH should address this.

Update:
About 2 weeks later, DTC 3157 returned intermittently. Shortly after, the tractor would not crank intermittently and show a low battery voltage (~11.6 V) on the ADIC. When it would crank, the engine would start, but die seconds later. Sometimes it would start and run normally. Eventually, I was able to diagnose a fault in the ignition switch and replaced it. At the same time I replaced the ECU relay K-001 and the Cranking relay K-002. The ignition switch had failed - there is no doubt about that.

The unit is now starting & running "tip-top"; I would even say "like new". Displaying normal voltage (~12.6 V) consistently.

Note:

• The original ignition (#84280152) has been discontinued and the current part is #90414993.
• I replaced the OE Omron relays with sealed units.
• To replace the ignition switch, it isn't necessary to pull the steering wheel. However, it is necessary to remove the shuttle lever and hand throttle knob in order to lift the dash cowl enough to access the ignition switch.

Hope this helps!

 

[klancf51]

See Update above.

 

[MikeB22]

I had almost the same exact intermittent starting issue with my 70A. Although no codes were ever indicated. After testing and replacing some of the safety start switches and seeming to start and run most of the time, It stopped one day and became a permanent no-start. At this point it was easy to trouble-shoot. Traced it to the ignition relay #2 in the main fuse block.

Update, one year later 10/2025 similar intermittent no start issues reoccurred. Suspecting another relay issue I bought a relay tester tool. (Electronic Specialties relay buddy #190) and sure enough ignition relay #1 failed intermittently. Upon testing all the other relays, five others were bad. Obviously this is poor quality, defective manufacturing. I replaced all relays with NAPA / ECHLIN brand relays part #: ECH AR172 and have had no further issues.

Hope this helps

 

[MikeB22]

This is the relay tester

 

[klancf51]

I had almost the same exact intermittent starting issue with my 70A. Although no codes were ever indicated. After testing and replacing some of the safety start switches and seeming to start and run most of the time, It stopped one day and became a permanent no-start. At this point it was easy to trouble-shoot. Traced it to the ignition relay #2 in the main fuse block.

Update, one year later 10/2025 similar intermittent no start issues reoccurred. Suspecting another relay issue I bought a relay tester tool. (Electronic Specialties relay buddy #190) and sure enough ignition relay #1 failed intermittently. Upon testing all the other relays in the fuse box, five were defective. Obviously this is poor quality, defective manufacturing. I replaced all relays with NAPA / ECHLIN brand relays part #: ECH AR172 and have had no further issues.

Hope this helps

The OMRON G8V-RH-1C7T-R-12VDC (CNH #84561098- discontinued) are the OE relays on my unit. They were rated at 35A (continuous) and 90A (inrush) @12VDC on the N.O. contacts, electrical endurance 100,000 operations, not sealed (i.e. not washable). An aftermarket replacement should meet or exceed those ratings. I'm not certain about the various ratings for the superseding relay, CNH #87696396 except that 35A@12VDC appears to still be the continuous current rating.

ECH AR172 is rated for 20A@12VDC. That's a 57% continuous current de-rating. Just a heads up on that.

 

[MikeB22]

Thanks, good info. According to Echlin, when you do a cross-reference of the Omron part number it indicated the ECH AR172. That is why I went with those. I'll see how long these last and if needed, replace with the CaseIh 87696396 or perhaps the NAPA AR533 that are 25Amp. I was just leary of ordering from Case, fearing I would get more of the Omron junk. What did you use as an Omron replacement?

 

[klancf51]

Thanks, good info. According to Echlin, when you do a cross-reference of the Omron part number it indicated the ECH AR172. That is why I went with those. I'll see how long these last and if needed, replace with the CaseIh 87696396 or perhaps the NAPA AR533 that are 25Amp. I was just leary of ordering from Case, fearing I would get more of the Omron junk. What did you use as an Omron replacement?

The life expectancy is largely dependent on voltage and the characteristics of the electrical load. Environment plays in this too. Per the OMRON G8V-RH datasheet, the contacts are rated for 12VDC, but with engine running the normal voltage is 13.7 - 14.7 VDC. Just saying...

After reviewing the datasheets of several ISO 280 type relays,
I selected 301-1C-S-R1-12VDC (datasheet attached). In addition to meeting the OMRON G8V-RH current ratings, I liked the 14 VDC load rating and that it was available for purchase in a sealed unit. It would not surprise me one bit if CNH #87696396 is a 301 family relay. Maybe someone knows?

 

[MikeB22]

Much appreciated. You really did your homework on this. Very impressive! So far the ECH AR172 that I installed over a year and 400 hours ago, is working fine. I will check back here occasionally with any updates. Thanks again for your wisdom!