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Error Code 42 Ignition Bypass Circuit Error


Tom Stacy

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Has anyone experienced this error code on their Esprit? Symptom is after starting, idles high, drops to 1200-1400RPM, then sputters and eventually stalls. Did this to me while driving for 10 minutes or so. Read code as DTC-42 : Ignition bypass Circuit error. I thought about replacing the IAC and TPS since both could cause this condition, but error code tells me that it may be ECM related. Any thoughts from experience out there?
Thanks.
Tom S.
'89 Lotus Esprit Turbo x180

'89 Lotus Turbo Esprit x180

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There's a list of the error codes in the Freescan manual which is available from here...

https://www.thelotusforums.com/freescan_manual.pdf

Code 42 ELECTRONIC SPARK TIMING (EST) CIRCUIT Ignition module sends a reference signal to the ECU when engine is cranking or running. When under 700rpm. The ignition modules controls the ignition timing. When the engine speed exceeds 700rpm the ECU send a 5 V signal to switch the timing to ECU control. An open or ground in the EST bypass circuit will set a Code 42. Engine will run in “limp home” or “bypass” timing.

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  • 4 weeks later...

Tested EST circuitry, no opens or shorts. Ran Freescan, reviewed data, nothing out of the ordinary except IAC stuck at 170. Swapped IAC, ran freescan and found no longer stuck but error 42 still persists with rough idle and stall. Removed ECU, swapped out with spare unit and installed MemCal chip. Started car, idle immediately leveled out at 1350RPM, with no stalling. Faulty ECU was the issue for code 42. Will buy another spare on EBAY to keep on hand.

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'89 Lotus Turbo Esprit x180

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Probably not inexpensive as you say, but they are cheap enough and available on EBAY. I found one (#1228707) for under $25 and free shipping. Can't beat it, worth the investment for future insurance.

TS

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'89 Lotus Turbo Esprit x180

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