But activity was muted ahead of a holiday weekend in the UK, which will see markets closed on Monday.
The FTSE Euro Corporate Bond Index showed investment-grade corporate bonds in euros yielding an average 47.8 basis points more than similarly dated government bonds at 1555 GMT, 0.8 basis point less on the day.
"Overall the market is firmer although US auto bonds have slipped this afternoon but there isn't a lot of trading going on, it is very quiet," said one trader.
"Next week we have US auto sales and we usually get some volatility in auto bonds ahead of those. The numbers are expected to be quite weak so we may well try and push wider."
Key US auto sales figures for August are due out on Wednesday. Auto sales heated up again in July, after a surprising slowdown a month earlier, buoyed by high incentives and low interest rates but analysts say the fourth quarter forecasts will be of most interest.
"The most important numbers in the (auto sales) presentation next week will be the fourth-quarter production forecast. With GM, everyone is looking to see whether they cut production, and if they do, by how much," said Alistair McCreadie, credit analyst at ABN AMRO.
"I would expect that most people will be pricing in a production cut from GM, but even if they announce a cut no-one will know what it means to their ratings. There will be nervousness around it until we hear from S&P."
GM bonds lost earlier this month on market speculation that credit rating agency Standard & Poor's would cut its rating.
S&P said on August 11 that weak auto profits this year were unlikely to warrant a debt rating downgrade, but it may cut GM's rating closer to "junk" over the next two years if profits from its auto business fail to improve.
Elsewhere, telecom bonds were around a basis point tighter, a trader said, after spreads narrowed up to 10 basis points in the past week.
"There are not a huge amount of flows today, after a phenomenal week," said the trader. "Telecoms have been boosted by the hope of higher credit ratings, especially Telecom Italia."
S&P said on Tuesday that it could raise its rating on the Telecom Italia in the next 12 months if it keeps its debt at about 30 billion euros. It rates the company BBB+ with a positive outlook.
In the high-yield market, bonds of German automotive systems maker Schefenacker AG fell after the company reported a pre-tax loss of 4.4 million euros compared to a profit of 14.8 million in the same period last year.